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GRADE 12 LEARNERS’ CONCEPTUAL UNDERSTANDING OF CHEMICAL
REPRESENTATIONS
by
ALEYAMMA JOSEPH
MINOR-DISSERTATION
submitted in partial fulfillment of the
requirements for the degree
MAGISTER EDUCATIONIS
in
SCIENCE EDUCATION
in the
FACULTY OF EDUCATION
at the
UNIVERSITY OF JOHANNESBURG
Supervisor: DR U Ramnarain
Co - Supervisor: DR JJJ de Beer
November 2011
i
DECLARATION
I, Aleyamma Joseph, declare that the work contained in this Minor-Dissertation
entitled GRADE 12 LEARNERS’ CONCEPTUAL UNDERSTANDING OF CHEMICAL
REPRESENTATIONS is my own work and all the sources I have used or quoted
have been indicated and acknowledged by means of references.
Signature: __________________________
Aleyamma Joseph
Johannesburg
November 2011
ii
DEDICATION
To my late dearest dad,
Mr. N.D Mathew
iii
ACKNOWLEDGEMENTS
I would like to express my sincere thanks and gratitude to the following people for
their outstanding and valuable contributions throughout my research study:
• DR. U. Ramnarain, my supervisor for his guidance, supervision and
assistance without which it could not have been possible to present this work
as it is. I am grateful for his patience, understanding, care and continued
support.
• University of Johannesburg statistical services for their support and
assistance in getting this work completed.
• I would also like to express my sincere thanks to everybody who directly and
indirectly assisted me to complete this work.
• My husband, Dr. V. K. Joseph and children, Suja, Daniel, Sheeba and Jerry,
for their support and assistance without which I couldn’t complete this work.
• Above all, to my Lord and Saviour, Jesus Christ, I am grateful and humbled by
the bountiful blessings you continue to bestow on me.
iv
SYNOPSIS
The education system in this country has undergone tremendous changes in the last
few years with the intention of transforming it into a competent education system that
can match and be equivalent to the global standards. In spite of all the changes, the
underperformance of learners and schools in the National Senior Certificate
examination, especially in the critical subjects such as mathematics and physical
sciences is a serious challenge to all stakeholders of education. The national pass
rate for physical science was 55% at national level and 64.5% at the Gauteng
Provincial level in the Grade 12, 2008 national examination.
The examination results published in the past three years reflects that there is no
significant improvement in the performance of learners in the physical sciences
examination. In view of the above it will be appropriate to explore new strategies and
ways to enable learners to achieve the desired outcomes at a higher level in physical
sciences.
The aim of this study is to investigate the conceptual understanding of chemical
representations by grade 12 learners. A quantitative research method was utilised to
determine the performance of Grade 12 learners in responding to questions at the
macroscopic, microscopic and symbolic levels of chemical representations. A
sample of five hundred randomly selected learner scripts from the 2008 National
Senior Certificate examination were used for the script analysis and data collection.
A second phase of qualitative research method was used to collect and analyse data
to describe how teachers facilitate learner conceptual understanding at the
macroscopic, microscopic and symbolic levels of chemical representation. Three
teachers from previously disadvantaged schools were selected to participate in this
research study. Interviews and class observations were conducted to collect data for
this phase of study.
The findings indicate that the grade 12 learners have a poor conceptual
understanding of macroscopic, microscopic and symbolic levels of chemical
representations. This lack of understanding is reflected in their poor performance in
answering questions in the NSC chemistry examination of 2008. Teachers have a
limited conception of the three levels of chemical representations and they lack
v
effective teaching strategies to facilitate the learning of concepts at the levels of
chemical representations. This poor facilitation of concepts by teachers at classroom
levels has a negative impact on the level of understanding by learners and hence,
they perform poor in the grade 12 NSC examination.
To improve the performance of grade 12 learners in the NSC examination it is
recommended that the Department of Basic Education initiate in-service courses for
physical sciences teachers in chemistry. This should be done with a view to
developing teacher knowledge and understanding of the levels of chemical
representation to enable them to more explicitly fashion strategies in facilitating the
learning of concepts at these levels.
vi
Table of Contents
DECLARATION i
DEDICATION ii
ACKNOWLEDGEMENTS iii
SYNOPSIS iv
Table of Contents vi
LIST OF TABLES x
LIST OF FIGURES x
LIST OF APPENDICES xii
CHAPTER ONE 1
OVERVIEW OF THE STUDY
1.1 INTRODUCTION 1
1.2 LEVELS OF CHEMICAL REPRESENTATION 7
1.3 RATIONALE FOR STUDY 9
1.3.1 My own experience as a marker for the subject 10
1.3.2 Reports from the moderators and examiners 10
1.3.3 Research on chemistry learning and teaching 14
1.4 PROBLEM STATEMENT AND RESEARCH QUESTIONS 14
1.5 AIMS AND OBJECTIVES OF THE STUDY 15
1.6 RESEARCH METHODOLOGY 16
1.7 COMPLIANCE WITH THE ETHICAL STANDARDS 16
1.8 DIVISION OF CHAPTERS 17
1.9 CONCLUSION 18
CHAPTER TWO 19
LITERATURE REVIEW AND THEORETICAL BACKGROUND 19
2.1 INTRODUCTION 19
2.2 CHEMICAL REPRESENTATION OF MATTER 19
2.2.1 The Three Levels of Chemical Representation of Matter 20
2.3 THEORETICAL AND CONCEPTUAL FRAME WORK 23
2.3.1 Piaget and constructivism 23
2.3.2 Vygotsky and Social Constructivism 24
2.4 CONCEPTUAL UNDERSTANDING IN CHEMISTRY 25
2.4.1 Conceptual nature of chemistry as a discipline 26
2.4.2 Difficulties in chemistry learning 26
vii
2.4.3 Conceptual understanding and language 28
2.5 CHEMISTRY TEACHING 30
2.5.1 Pedagogical Content Knowledge in Science 31
2.5.2 Learner Centred Teaching 32
2.5.3 Conceptual Change Perspective to Teaching 32
2.5.4 Problem Solving Approach and Teaching 33
2.5.5 Cooperative Learning as a Teaching Strategy 35
2.5.6 Practical / Laboratory work as a Teaching Strategy 36
2.6 THE NATIONAL GRADE 12 EXAMINATION 37
2.6.1 Assessment in the grade 12 NSC examination 37
2.6.2 Learner attainment in physical sciences 40
2.7 CLASSIFYING QUESTIONS IN THE 2008 NCS CHEMISTRY EXAMINATION
PAPER INTO LEVELS OF CHEMICAL REPRESENTATION 41
2.8 CONCLUSION 45
CHAPTER THREE
RESEARCH DESIGN AND METHODOLOGY
3.1 INTRODUCTION 46
3.2 RESEARCH QUESTIONS AND OBJECTIVES 46
3.3 RESEARCH DESIGN AND METHODOLOGY 47
3.3.1 Quantitative Research 47
3.3.2 Qualitative Research 48
3.4 PREPARATION OF THE TOOL FOR DATA COLLECTION 49
3.5 DATA COLLECTION 51
3.6 SAMPLING 53
3.7 ANALYSIS OF DATA 54
3.8 RELIABILITY AND VALIDITY 57
3.9 CONCLUSION 58
CHAPTER FOUR 59
QUANTITATIVE ANALYSIS OF THE EXAMINATION SCRIPT DATA 59
4.1 INTRODUCTION 59
4.2 CLASSIFICATION OF QUESTIONS ACCORDING TO LEVELS OF
CHEMICAL REPRESENTATIONS 60
4.2.1 Format of NSC, Chemistry question paper 60
4.2.2 Classification of questions according to levels of chemical representation 60
viii
4.2.3 The weighting of the classification 61
4.3 STATISTICAL ANALYSIS OF THE DATA 62
4.3.1 Descriptive for Percentage Acquired 62
4.3.2 Distribution of percentages acquired 63
4.3.3 Summary of the descriptive statistics for all seven categories 64
4.3.4 Comparative box-and-whisker plot 72
4.3.5 Analysis of variance 73
4.4 ANALYSIS OF LEARNER PERFORMANCE AND RESPONSES TO
QUESTIONS AT LEVELS OF REPRESENTATION 76
4.4.1 Macroscopic category of classification 77
4.4.2 Sub-microscopic category of classification and learner performance 79
4.4.3 Symbolic category of classification and learner performance 79
4.4.4 Macroscopic↔ sub-microscopic category of classification and learner
performance 84
4.4.5 Macroscopic↔ symbolic category of classification and learner
performance 85
4.4.6 Sub-microscopic ↔ symbolic category of classification and learner 87
performance 87
4.4.7 Macroscopic ↔ Sub-microscopic ↔ symbolic category of classification
and learner performance 90
4.5 CONCLUSION 92
CHAPTER FIVE 94
QUALITATIVE DATA ANALYSIS
5.1 INTRODUCTION 94
5.2 PARTICIPANTS IN THE STUDY 94
5.2.1 Teacher profile 94
5.2.2 School profile 95
5.3 PRE-INTERVIEW 96
5.3.1 Themes and sub-themes of pre-interview 96
5.3.2 Analysis of Data Collected During Pre- Interview 97
5.3.2.1 Teachers maintain that learners find chemistry concepts to be abstrcat 98
5.3.2.2 Teachers use a variety of strategies in facilitating conceptual
understanding in chemistry 99
5.3.2.3 Teachers bemoaned the lack of physical resources in experiments in
ix
chemistry 102
5.4 LESSON OBSERVATION 103
5.4.1 Lesson observation: Mrs Khumalo 103
5.4.2 Lesson observation of: Mr Mashigo 105
5.4.3 Lesson observation of: Mrs Mbele 108
5.4.4 Trends in classroom observation 110
5.5 CONCLUSION Error! Bookmark not defined. 111
CHAPTER SIX 112
FINDINGS AND RECOMMENDATIONS 112
6.1 INTRODUCTION 112
6.2 OVERVIEW OF THE RESEARCH 112
6.3 SUMMARY OF THE IMPORTANT FINDINGS 113
6.3.1 Findings from the analysis of chemistry examination scripts 113
6.3.2 Findings from interviews and class observation of educators 116
6.4 RECOMMENDATIONS 117
6.5 SCOPE FOR FURTHER STUDY 118
6.6 CONCLUSION 118
BIBLIOGRAPHY 119
x
LIST OF TABLES
Table 1.1: Trends in the Physical Science pass rate for all schools: 2008-2010 3
Table 1.2: Number passing physical sciences at different levels 4
Table 1.3: Content for the grade 12 Physical Sciences examination 6
Table 1.4: Summary of the report by the moderators and examiners (2008 NSC)
chemistry examination 11
Table 2.1 Weighting of Cognitive Levels 38
Table 2.2: Weighting of learning outcomes 38
Table 2.3: Mark allocation of question paper, P2: Chemistry 39
Table 2.4: Format of grade 12 NSC P2 Chemistry 39
Table 2..5: Learner Achievement Level 40
Table 3.1: Categorization of levels of representation in chemistry 50
Table 4.1: Classification framework of chemical representations 61
Table 4.2: The weighting and percentage distribution 62
Table 4.3: Descriptive for percentage acquired 63
Table 4.4: Descriptive for percentage acquired per question in each of the seven
levels 65
Table 4.5: Tests of Normality 74
Table 4.6: Test of homogeneity of variances 75
Table 4.7: ANOVA 75
Table 4.8: Test statistics ab 76
Table 4.9: Macroscopic category of classification 77
Table 4.10: The sub-microscopic category of classification 80
Table 4.11: The symbolic category of classification 81
Table 4.12: Macroscopic sub-microscopic category of classification 84
Table4.13: Macroscopic symbolic category of classification 85
Table 4.14: Sub-microscopic symbolic category of classification 87
Table 4.15: Macroscopic sub-microscopic symbolic category of
classification 91
Table 5.1: Profile of teachers 95
Table 5.2: Themes and sub-themes of pre-interview 97
xi
LIST OF FIGURES
Figure 1.1 Percentage of candidates who achieved (30% and above and 40% and
above in selected subjects in 2010 5
Figure 2.1: Three levels of representations used in Chemistry 20
Figure 2.2: Examples of the three levels of representations used in Chemistry 22
Figure 3.1: First phase of data collection 55
Figure 3.2 : Representation of the research method 56
Figure 4.1 : Distribution of percentages acquired 64
Figure 4.2: Descriptive statistics for macroscopic level 68
Figure 4.3: Descriptive statistics for sub-microscopic level 69
Figure 4.4: Descriptive statistics for symbolic level 69
Figure 4.5: Descriptive statistics for macroscopic to sub-microscopic level 70
Figure 4.6: Descriptive statistics for macroscopic to symbolic level 70
Figure 4.7: Descriptive statistics for sub-microscopic to symbolic level 71
Figure 4.8: Descriptive statistics for macroscopic to sub-microscopic to symbolic
level 71
Figure 4.9: Comparative box-and-whisker plot 73
xii
LIST OF APPENDICES
APPENDIX DESCRIPTION PAGE
Appendix A Ethical Clearance 139
Appendix B Permission letter to conduct research from GDE 140
Appendix C Letter of consent 142
Appendix D NSC Chemistry Question Paper 2008 P2 143
Appendix E Interview schedule 162
Appendix F Pre-interview Transcripts 163
Appendix G Lesson Observation Transcripts 194
1
CHAPTER ONE
1. OVERVIEW OF THE STUDY
1.1 INTRODUCTION
The education system in this country has undergone tremendous changes in the last
few years with the intention of transforming it into a competent education system that
can be equivalent to the global education standards. Amongst other changes, the
introduction of the National Curriculum Statement (NCS) can be regarded as the most
noticeable and important change that affected all stakeholders in education especially
the learners. The introduction of the NCS is aimed at equipping learners, irrespective of
their socio-economic background, race, gender, physical ability or intellectual ability,
with knowledge, skills and values necessary for self-fulfilment and meaningful
participation in society as a citizen of a free country (Department of Education, 2005). It
is also aimed at meeting the challenges posed by the scale of change in the world, the
growth and development of knowledge and technology and the demands of the 21st
century that require learners to be exposed to different and higher levels of skills and
knowledge (Department of Education, 2005).
In-spite of all these changes, the underperformance of learners and schools in the
matric (grade 12) examination, especially in the critical subjects such as mathematics
and physical sciences is a serious challenge to all stakeholders in education. The high
failure rate of learners in physical sciences has a direct impact on the training and
supply of skilled people to the human resource of this country. The shortage of skilled
people in our country seriously affects the economic growth and the technological
advancement of the nation. There is evidence of a growing skills shortage with a
possible shortfall of between 1.5 and 2 million skilled people over the next ten years in
the country (Burtenshaw, 2006). South Africa produces about 1400 engineering
2
graduates every year and this needs to be expanded to at least 2400 to close the
shortfall (Barnes, 2007).
The secondary school education system plays an important role in addressing the
problem of skills shortage in this country. Schools are expected to provide appropriate
career and support to learners in selected subjects that are relevant and that will open
enormous opportunities for the learners to pursue their education in the engineering,
technology and other areas at the tertiary level. In view of the extremely high shortage
of engineers and skilled personnel in the country, educational institutions such as the
schools have a huge responsibility of encouraging more learners to take physical
sciences and mathematics as their choice of subjects in their subject groups that will
pave the way to pursue their studies in the engineering and scientific fields.
However, the national pass rate for physical sciences was 55% at the national level and
64.5% at the Gauteng provincial level in the grade 12, 2008 national examination. This
was the first national grade 12 examination based on the NCS. As a result of the low
pass rate an inadequate number of learners are entering tertiary institutions to register
for engineering and other related courses and hence the national crisis of skill shortage
still remains as a major stumbling block for the nation’s progress and prosperity. This
led to the Department of Education (DoE) commissioning the University of
Johannesburg (UJ) to conduct an exam script analysis to investigate the poor
performance of learners in the 2008 grade 12 physical sciences examination. I
participated in the project as a student researcher. In this exam script analysis project, I
focused on the performance of learners in chemistry.
The performance of learners in the matric examination is always in the public domain as
it is a stepping stone for learners to enter into the higher education field to further their
education. This performance is very often used to establish the status of the basic
education system in the country and it can be used to ascertain the quality of curriculum
delivery at various schools. The matric (grade 12) results are used as the main indicator
of the quality of the education system and so there is a reasonable concern about the
3
current state of education (UMALUSI, 2010). The low pass rate and underperformance
of learners in the matric examination is a serious concern for all stakeholders in
education. The examination results published in the past three years reflect that there
is no significant improvement in the performance of learners in the physical sciences
examination. Classification such as higher grade, standard grade and lower grade were
used to register for different subjects in the matric examination in the old system
(NATED 550). Learners who passed their matric examination with their subjects on the
higher grade were able to access the universities to further their education. However,
the new curriculum has eliminated the above classification and it gives equal
opportunities for all learners to continue their education. The new curriculum offers all
subjects at one level; consequently there is no longer a distinction between subjects on
a higher, standard or lower grade (Neil & Kistener, 2009) and all learners write the same
paper irrespective of their cognitive levels and understanding.
Table 1.1: Trends in the Physical Science pass rate for all schools: 2008-2010
Source: UMALUSI Report (2010: 58)
It is evident from the above table that the performance of learners in physical sciences
remained relatively low for the past three years. It can also be observed that there is no
significant improvement in the pass rate despite all the interventions.
Year
No. Wrote
Phys. Sciences
(NSC)
No. Passed
Phys. Sciences
(NSC)
Percentage
Passed
(% achieved
at 30% and
above)
2008 218 156 119 823 54.9
2009 220 882 81 356 36.8
2010 205 364 98 260 47.8
4
Table 1.2: Number passing physical sciences at different levels
Year Wrote Passed at
30%
Passed
at 40%
Passed at
50%
Passed at
60%
Total not
passed
2008 218 156 119 823 61 480 32 524 16 620 98 042
2009 220 882 81 356 45 452 22 329 10 308 139 450
2010 205 364 98 260 60 917 30102 11560 107104
Adapted from UMALUSI Report (2010:67)
Table1.2 displays the performance of learners in the physical sciences examination at
different levels for the years 2008, 2009 and 2010. It can be noticed that less than 10%
of the total learners in each year are attaining a pass with 60% in the subject while
majority of the learners pass at 30%. This is an indication of the quality of the results
produced each year in the matric examination.
5
Figure 1.1 Percentage of candidates who achieved 30% and above and 40% and above in selected subjects in 2010
Source: UMALUSI (2010:56)
The graph above indicates that only 30% of the learners who wrote the 2010 NSC
examination managed to obtain 40% and above in the physical sciences examination.
The performance of learners in mathematics is similar to that of physical sciences. This
implies that the country is still faced with the situation where there is an unsatisfactorily
low number of matriculants who meet the requirements to pursue studies in science and
engineering at university. It is of interest to stakeholders such as the Department of
Basic Education (DBE), and in particular subject advisors and teachers to understand
why the performance of learners in physical sciences remains poor. Higher Education
South Africa (HESA, 2010) remains concerned about the performance of the key
subjects, in the domains of economic and management sciences and the natural
sciences.
Therefore, it is evident from the above discussion that there is no significant
improvement in the pass rate as well as the level of attainment of learners in the
6
physical sciences examination. The performance of learners declined from 54.9% in
2008 to 36.8% in 2009, but improved to 47.8% in 2010. However, the quality of pass
remains critically low. Based on this analysis it would therefore appear that the
introduction of the new curriculum did not result in any significant improvement in the
performance of the learners. Physical sciences as a subject in the NCS is divided into
six knowledge areas:
• Mechanics;
• Wave, sound, and light;
• Electricity and magnetism;
• Matter and materials;
• Chemical change; and
• Chemical systems
In the grade 12, NSC examination, physical sciences is examined in two separate
papers, namely paper 1 (physics) and paper 2 (chemistry). The knowledge area of
these individual papers is indicated in Table 1.3 below.
Table 1.3: Content for the grade 12 Physical Sciences examination
PAPER 1: PHYSICS FOCUS
PAPER 2: CHEMISTRY FOCUS
• Mechanics
• Waves, sound and light
• Electricity and magnetism
• Matter and materials
(optical phenomena and
properties of materials
mechanical properties)
• Chemical change
• Chemical systems
• Matter and materials
(organic molecules,
organic macromolecules)
7
This study focuses in particular on chemistry learning and teaching in grade 12 physical
sciences. Science education occupies a dominant and highly influential position in the
education system of the growing world. However the performance of learners in the
physical sciences examination is very poor. Chemistry is an important discipline in the
field of science (Aghadiuno, 1995). Most of the general chemistry content, at the high
school and university levels, is still taught and assessed in terms of facts, algorithms
and procedural knowledge without emphasis on conceptual understanding (Hesse &
Anderson, 1992). This study investigates the conceptual understanding of chemical
representations by grade 12 learners, as well as how teachers facilitate conceptual
understanding at the levels of chemical representation.
1.2 LEVELS OF CHEMICAL REPRESENTATION
For many learners, chemistry is regarded as extremely challenging in the science
curriculum. Teachers have to use chemical representations very often in their lessons to
make most of the concepts understandable to the learners. This is due to the fact that
many of the concepts in chemistry are abstract and teachers have to use models,
symbols and other forms of representations to help learners translate most of the
concepts into concrete knowledge. Representations are used to assist the learner to get
a better comprehension of concepts, however, the research findings exhibited that
learners do not always comprehend the role of the act of representing taken by the
teacher (Treagust, Chittleborough & Mamiala, 2003). According to Johnstone (1982),
chemical representations are observed in three levels: the macroscopic level which is
the observable level of a chemical reaction, the symbolic level represents the reaction
equations, symbols and formulae and the sub-microscopic level that refers to the
molecular properties of the elements or compounds. The macroscopic level is an
observable chemical phenomena and this can include experiences from learners’
everyday lives such as colour changes, observing new products being formed and
others disappearing. In order to communicate about these macroscopic phenomena,
chemists commonly use the symbolic level of representation that includes pictorial,
algebraic, physical and computational forms such as chemical equations, graphs,
8
reaction mechanisms, analogies and model kits. The sub-microscopic level of
representation which is based on the particle theory of matter is used to explain the
macroscopic phenomena in terms of the movement of particles (Treagust et al., 2003).
Molecular properties are too abstract and as a result a negative attitude has developed
about chemistry with learners claiming chemistry is boring (Stocklmayer & Gilbert,
2002).
Researchers have shown that learners have non-scientific conceptions at all three
levels and are not able to move from one level to another (Ben-Zvi, et al., 1986, 1987).
In order to develop understanding of chemical representations, learners need to have a
deeper understanding of chemical concepts. Many researchers (Gabel, 1999; Kozma,
2003; Tasker, 2000) have found that conceptual understanding in chemistry involves
being able to represent and translate chemical problems using all three forms of
representations- macroscopic, sub-microscopic and symbolic. For meaningful learning
to occur, the learning process needs to engage learners in an active manner such as
processing data, making inferences and comparisons, developing skills, generating
hypothesis, testing ideas, finding patterns, asking questions and reflecting on what they
have learned (Skamp, 1996). Chittleborough (2004) points out that there are a multitude
of factors that influence learning and make it more meaningful such as recognizing,
understanding and addressing the problems. Conceptual understanding of chemical
concepts involves not just understanding of each representations but also how they are
linked together (Kozma, 2003).
The teaching and learning of chemistry is around the concept of different levels of
representations and how to relate these levels. When a learner is unable to understand
the concepts, he/she is unable to achieve the learning outcomes and results in failure in
the chemistry examination. The development of learners’ understanding from a
procedural (knowing how) to a conditional level (knowing why) could be aided by linking
chemical concepts at the macroscopic level with the symbolic and sub-microscopic level
(Treagust et al., 2003).
9
Several studies have been conducted on the relationship between the teacher’s
pedagogical content knowledge and their teaching strategies. According to Vygotsky,
collaborative teaching could be applied for effective quality curriculum delivery. For
secondary school learners, shifting mentally between the macro and micro levels is
usually problematic, where as their teacher is often unaware of learners’ difficulties of
learning in this domain (De Jong, van Driel, & Verloop, 2002). According to De Jong et
al, (2002) the two following elements are central in any conceptualization of pedagogical
content knowledge (PCK), that is, knowledge of representation of subject matter and
instructional strategies and an understanding of specific learner conceptions and
learning difficulties on the other hand. A teacher’s development of PCK depends on
various factors such as knowledge of subject matter (Smith, & Neale, 1989); teaching
experience with respect to specific topics (Lederman, GessNewsome, & Latz, 1994);
knowledge of learners’ conceptions and learning difficulties (Geddis, 1993; Lederman et
al., 1994; van Driel, Verloop, & De vos, 1998) and participating in specific workshops
(Clermont, Krajcik, & Borko, 1993).
1.3 RATIONALE FOR STUDY Conceptual questions are higher-order questions that require higher-order thinking skills
or higher-order cognitive skills (HOCS) to invoke learners’ deep understanding of
chemical concepts (Huddle, 1998; Nurrenbern & Robinson, 1998; Zoller, Lubezky,
Nakhleh, & Dori, 1995). Deep understanding generally refers to how concepts are
represented in the learner’s mind and more importantly how these concepts are
connected with each other (Grotzer, 1999). Most of the theories and concepts that are
taught in chemistry are abstract and hence analogies or models are used to represent
and to make the concepts more understandable. Schools are expected to have the
minimum resources available in their laboratories to be used by the physical sciences
teachers to make such representations whenever it is necessary in the chemistry
lessons. Using such representations more frequently in the lessons make them
interesting and simple for the learners. Chemistry is commonly exhibited at three
different levels of representation namely macroscopic, sub-microscopic and symbolic
10
levels that combine to enrich the explanations of chemical concepts (Treagust et al.,
2003). In order to inculcate a deep understanding of chemical representations in
learners, teachers need to have good pedagogical content knowledge (PCK). In view of
these three levels of chemistry as described in literature this study investigates the
performance of grade 12 learners at these levels in a national physical sciences
examination. I will also describe how teachers facilitate learner conceptual
understanding at the macroscopic, sub-microscopic and symbolic levels of chemical
representation. Below I will motivate for doing this study in terms of my own experiences
as an experienced marker in the national grade 12 physical sciences examination,
reports from moderators and examiners, and research that has been conducted in
chemistry learning and teaching.
1.3.1 My own experience as a marker for the subject
I have been a senior marker of grade 12 Senior Certificate as well as National Senior
Certificate (NSC) physical sciences examination papers for many years. My observation
of learner performance is that they appear to have particular difficulty with the chemistry
paper. In many cases learners are failing to answer questions related to conceptual
understanding. The moderator’s report (2008, 2009 and 2010) on the chemistry paper
shows that learners are struggling to answer chemistry questions. This aroused my
interest to carry out this research on chemical representations which will assist me to
explore and study the level of understanding of concepts by the learners.
1.3.2 Reports from the moderators and examiners
NSC examination question papers are set nationally and quality assured by UMALUSI,
the Council for Quality Assurance in the General and Further Education and Training.
Both the internal and external moderators evaluate the question papers by using a set
of criteria developed by UMALUSI such as Adherence to Assessment
Policies/Guideline Documents, content coverage, cognitive skills, language and bias,
11
predictability, marking memorandum/ guideline, technical criteria, internal moderation,
and overall impression of the paper ( DBE, 2009).
By the introduction of NCS, question papers for all subjects have been set nationally by
a panel of examiners which are then moderated by a panel of moderators. Finally, the
question papers have to be approved by external moderators appointed by UMALUSI.
The papers need to be evaluated for compliance with policies and guidelines, content
coverage, cognitive skills, language usage, predictability, technical criteria and suitability
of marking guidelines (DoE, 2008). After each public examination, the chief markers and
internal moderators compile reports during the marking session of the scripts of
candidates who wrote the NSC examination. These reports provide all stakeholders of
the education system with valuable quantitative as well as qualitative information of the
learner performance and also highlight those areas that have been identified as
problematic, based on the responses of candidates (DBE, 2011). These reports also
identify the aspects of curriculum that have been problematic, and suggestions are
made for improvement in terms of teaching and learning and support to be provided for
teachers. Also these reports highlight the learners’ difficulties in achieving the intended
course outcomes (DBE, 2011). Below, I present a summary report by examiners and
moderators for the 2008 grade 12 chemistry examination.
Table 1.4: Summary of the report by the moderators and examiners (2008 NSC) chemistry examination
Question Comments
Section A Question 1-4: Even though it is basic recall questions, many learners
do not know the basic terminology and failed to answer. These
questions may benefit the learners with language barrier as it does not
involve too much reading. Multiple choice questions were answered
very badly.
Organic Question 5 &7: Many learners: (i) Cannot differentiate between the
12
chemistry concepts structural, condensed structural and semi condensed
structural formulae; (ii)have no knowledge of IUPAC system of naming
compounds and general formula of different homologous series; (iii) do
not know the three basic reactions in organic chemistry ; (iv) do not
have an understanding of the terminologies like hydration, bromination,
dehydrohalogenation, hydrogenation, etc. (vi) Struggle with functional
groups; and (vii) lost marks as they do not have an in depth knowledge
in organic chemistry.
Investigation
question
Question 6: The investigative question was from organic chemistry.
Many learners’ battled with this question due to the following reasons:
(i) no knowledge of testing an unsaturated compound (ii) They are
confused with formulating investigative question and hypothesis (iii)
They could not identify safety measures as they were not exposed to
practical work in the class room.
Reaction
rates
Questions 8: Learners do not know the collision theory and hence
failed to use the key words molecular orientation, sufficient kinetic
energy and effective collisions. They cannot read and interpret the
graph. Many learners knew the fact that an addition of a catalyst
reduces the activation energy of a reaction.
Equilibrium
question
Question 9: 9.1 is an LO3 question but learners could not answer it
due to lack of practice. They could not explain the effect of Le
Chatelier’s principle on the system. They still find problems in
determining the Kc value. Calculation of concentration, mole
conversion, is a problem. They could not write the Kc expression for
the reaction provided and did not substitute concentrations at
equilibrium. Majority of learners used the table method but
experienced big problems. Many of them were unable to explain effect
of temperature on Kc value.
Electro
chemistry
Question 10: Learners had difficulty in distinguishing between the
concepts oxidation, reduction, oxidizing agent and reducing agent.
They could not use the reduction table correctly and copied reactions
13
incorrectly. They used double arrows for half reactions and lost marks.
Calculation of electrode potential was a problem
Chemical
system
Question 11: This question examined an electrolytic cell as part of the
new content. A large number of students could not recognize that
electrolytic cell is the reverse of a galvanic cell and subsequently
reversed the relevant oxidation/reduction reaction. Learners could not
understand the formation of aluminium involves the conversion of
aluminium ions to aluminium atom. Lack of knowledge regarding the
formation of ions and atoms led learners in losing the marks. Learners
answered the LO3 section very badly.
Question 12: Learners had difficulty in using the flow diagram and LO3
questions were answered poorly as they did not have an idea of
nitrogen cycle. Many had difficulty in expressing their ideas due to
language barrier.
The above report clearly indicates that many learners could not differentiate between
the concepts, structural, condensed structural and semi condensed structural formulae.
They had no knowledge of the IUPAC system of naming compounds and general
formula of different homologous series. They also struggled with functional groups.
The report also revealed that learners had difficulty in interpreting the graphs as well as
understanding the role of a catalyst in reducing the activation energy of a reaction.
Learner’s difficulty in distinguishing between the concepts such as oxidation, reduction,
oxidizing agent and reducing agent was also revealed in the report. In general, the lack
of knowledge of most of the chemical concepts tested in the examination was exhibited
in the report. This report is a clear testimony to the fact that many of the learners had
very little understanding of the chemical concepts that were explained and taught in the
classrooms using the chemical representations.
14
1.3.3 Research on chemistry learning and teaching
A study conducted by Potgieter and Mashigoowitz (2010) to evaluate the level of
preparedness for tertiary chemistry studies of the 2008 matric cohort, concluded that the
new content material added to the grade 10-12 physical sciences curriculum resulted in
an overcrowded syllabus from 2008. It was indicated that the effective quality curriculum
delivery of such an overcrowded syllabus requires adequate physical and human
resources at every school. The effectiveness of school chemistry teaching is dependent
on the teacher’s ability to communicate and explain abstract and complex chemical
concepts, and on the learner’s ability to understand the explanations. Expert chemistry
teachers present new information at an appropriate level for the learner, make use of
relevant explanatory artefacts, build on the knowledge and concepts that learners
already understand, and provide learners with all the information that they need to know
without being beyond their grasp or over-simplifying the content (Treagust & Harisson,
1999). Teachers need to be cognizant of the three levels of representation and their
meaning because the manner in which chemistry is taught may cause learning
difficulties (Hussein & Reid, 2009). According to Johnstone (1991), most teachers use
the three levels of representation in their explanations without being aware of the
cognitive demands being made on learners. A secondary focus of my study is therefore
trying to understand how teachers facilitate chemistry understanding at these levels of
representation.
1.4 PROBLEM STATEMENT AND RESEARCH QUESTIONS
The complex and abstract nature of chemistry makes the study of the subject difficult for
learners (Ben-Zvi et al., 1987, 1988; Gabel, 1998, 1999; Johnstone, 1991, 1993;
Nakhleh, 1992; Treagust & Chittleborough, 2001). One of the reasons for the difficulties
that learners experience in understanding the nature of matter is the multiple levels of
representation that have already been described.
15
Teachers need to be cognisant of the three levels of representation, and their meaning.
The way chemistry is taught may cause major problems (Hussein & Reid, 2009).
According to Johnstone (1991) most teachers use the three levels of representation in
their explanations without being aware of the demands being made on the learners.
Harrison and Treagust (2002) make the point that there is a tension between teaching
macroscopic chemistry, which is generally hands on and viewed by learners as
interesting, and the difficulties of explaining macroscopic changes in terms of the
behaviour of sub-microscopic particles. Part of the tension has been ascribed to how
and when to deal with those three worlds in chemistry teaching that characterize
chemistry.
Accordingly, the following research questions are formulated:
1. What is the performance of grade 12 learners in responding to questions at the
macroscopic, sub-microscopic and symbolic levels of chemical representation as
demanded in a high stakes chemistry examination?
2. What strategies do teachers use in facilitating learner understanding at the
macroscopic, sub-microscopic and symbolic levels of chemical representation?
1.5 AIMS AND OBJECTIVES OF THE STUDY
The aim of this study is to investigate the conceptual understanding of chemical
representations by grade 12 learners. In order to realize the aim of the study, the
following objectives are set:
1. To determine the performance of grade 12 learners in responding to questions at the
macroscopic, sub-microscopic and symbolic levels of chemical representation.
2. To describe how teachers facilitate learner conceptual understanding at the
macroscopic, sub-microscopic and symbolic levels of chemical representation.
16
1.6 RESEARCH METHODOLOGY
The questions in the 2008 grade 12 chemistry examination were analyzed and
classified according to the chemical representation demanded by these questions. The
validity of this classification was established by having the questions reviewed by a
researcher in science education. Thereafter, I analyzed a random sample of 500 grade
12 scripts provided by the Gauteng Department of Education (GDE) for this
examination. The average performance of learners at each of the three levels of
chemical representation was calculated using excel software.
In researching the second aim of the study, a case study method was followed using a
qualitative approach to gain an in-depth understanding of the strategies teachers use in
facilitating the conceptual understanding of learners at the macroscopic, sub-
microscopic and symbolic levels of chemical representation. The cases were three
grade 12 physical sciences teachers from the Gauteng South district, the district where I
am the subject facilitator. I did class observations, and conducted interviews with the
teachers on the strategies they use at the three levels of chemical representation. Class
observations were video-recorded and interviews were audio-recorded. The interviews
and class observations were then transcribed and analysed. Qualitative data were
coded and classified, a process that involves breaking up data into bits and bringing it
together again in a new way. This process was guided by the conceptual framework for
the levels of chemical representation already mentioned. I sought to establish reliability
in this process of coding and grouping codes into families by asking a researcher in
science education to analyse the data using the same method, and then looking to see
the extent of agreement in our analysis.
1.7 COMPLIANCE WITH THE ETHICAL STANDARDS
Permission was obtained from the GDE, by request to conduct the research.
Permission was also granted from my District Director, the chosen school’s principals,
parents of learners and the three teachers who participated in this study. A verbal
17
explanation was given to the teachers on the aim and purpose of the study, and the
type of data needed from them.
Teachers and learners participated voluntarily and they were informed that they would
be able to withdraw at any stage of the process. On completion of the study a final
report was given to each participant as well as the principal and GDE. The participants
were informed that they would remain anonymous in all aspects of the study.
1.8 DIVISION OF CHAPTERS
Chapter one is the general outline of the research. It gives an introduction to the study,
background on the development of South Africa’s new education system, a brief
literature review, research question and aim of the study, significance of the research,
applications of the research and chapter outline with a conclusion.
Chapter two reviews the relevant literature in the field of study and concentrates on the
three levels of representations and various research studies in chemistry, conceptual
understanding at the macroscopic, sub-microscopic and symbolic levels of chemical
representation, conceptual change theory and how educators facilitate the process of
learner understanding.
The third chapter outlines the research design and methodology. This consists of
details of the collection of both quantitative and qualitative data used for the study. It
also explains the methods used to analyse the data.
In chapter four the data collected through the script analysis of the grade 12 learners’
examination scripts were analysed and interpreted using a quantitative research
methodology. A Classification Framework of Chemical Representation (CFCR) was
used to analyse and interpret the data obtained through the script analysis.
18
In chapter five, the strategies used by teachers to facilitate learner conceptual
understanding at the macroscopic, sub-microscopic and symbolic levels of chemical
representations were studied. A qualitative research methodology was used for the
collection and analysis of the data required for the study. Data was collected using
interviews and class observations.
Chapter six provides the summary, conclusion and recommendations of the research.
Reflections of the research are done in detail here. Guidelines to teachers from the
findings on how to improve the teaching strategy, limitations of the study and
recommended possible future studies are also discussed.
1.9 CONCLUSION
This chapter outlines briefly the representations in chemistry, learners’ conceptual
understanding of chemical representations and how teachers facilitate chemical
representations in their chemistry lessons. The background of the research study, the
context and rationale for the study, statement of the problem and the aim of the study
are also stated. Chapter 2 will focus on a detailed literature study of levels of
representations in chemistry, learners’ conceptual knowledge on chemical
representations, teachers’ content knowledge to facilitate learners’ conceptual
understanding of representations and theories that inform chemistry learning.
19
CHAPTER TWO
2. LITERATURE REVIEW AND THEORETICAL BACKGROUND
2.1 INTRODUCTION This chapter reviews the various forms of literature utilised to establish the objectives of
the research study. The primary focus of the study is grade 12 learners’ conceptual
understanding of chemical representations. In order to attain this, one must have a very
clear understanding of the deliverables and desirable outcomes of the current education
system in South Africa at the FET (Grade 10-12) level. In this chapter, I will firstly
provide an extensive review of literature on the chemical representations of matter, and
the learning of chemistry in relation to chemical representations.
Thereafter, I will highlight various means and strategies utilized by teachers to facilitate
learner conceptual understanding at the macroscopic, sub-microscopic and symbolic
levels of chemical representation. The chapter then outlines a detailed study of the
grade 12 NSC examination system in South Africa and concludes with a summary.
2.2 CHEMICAL REPRESENTATION OF MATTER
Chemistry is regarded as an abstract subject, and due to this nature, a deep
understanding and mastery within this field becomes much more difficult than within
other areas of the curriculum. Learning and understanding of chemistry is dependent on
clear explanations of abstract chemical concepts (Chittleborough, 2004). Models and
chemical representations are used in explaining scientific and chemical concepts to
enhance learning and understanding and developing learners’ mental models of
chemical concepts and sub-microscopic level of chemical representation of matter
(Johnson-Laird, 1983).
20
2.2.1 The Three Levels of Chemical Representation of Matter
The teaching and understanding of chemistry is based on the atomic theory of matter
which is an abstract concept. According to Johnstone (1982), chemical concepts and
phenomena can be explained at three levels of chemical representation of matter such
as the macroscopic, sub-microscopic and symbolic level (refer to figure 2. 1).
� The macroscopic level – comprises of tangible and visible chemicals which deal
with the learner’s real life experiences and observable chemical phenomena (e.g.
experiments, materials or pictures or illustration of materials etc).
� The sub-microscopic level – comprises of the particulate level that deals with the
real sub-microscopic particles, which cannot be seen directly such as electrons,
molecules, ions and atoms.
� The symbolic level - deals with the representations of chemical phenomena using
a variety of media including models, pictures, chemical equations, computer
models and structural formulae.
Figure 2.1: Three levels of representations used in chemistry
macroscopic
(features that are visible)
sub-microscopic (particles) symbolic (various representations of
chemicals)
Source: Johnstone, 1982. In: Chittleborough (2004: 18)
21
The three levels are inter-related and by the use of these three levels learners construct
their knowledge in chemistry. A learner’s understanding of the role of each level of
representation namely, microscopic, symbolic and sub-microscopic- as well as the
relationship between each level is often assumed by chemistry teachers who commonly
use all three levels simultaneously (Treagust et al., 2003). The macroscopic observable
chemical phenomena are the basis of chemistry and explanations of these phenomena
usually rely on the symbolic and sub-microscopic level of representations. Therefore,
the ability of learners to understand the role of each level of chemical representation
and the ability to transfer knowledge from one level to another is an important aspect of
generating understandable explanation (Treagust et al., 2003). The simultaneous use of
macroscopic, sub-microscopic and symbolic representations has been shown to reduce
learner’s alternative concepts (Russell, 1997). Research studies have shown that it is
essential for a teacher’s explanation to be “learner friendly” and compatible with the
learner’s explanatory knowledge.
Structural (symbolic) representations in chemistry refers to different types of formulas,
structures, computer models, chemical equations, ball & stick models and symbols used
in chemistry. The drafting of molecular structures and the writing of chemical formula
are namely ideology - laden and theory- laden (Hoffmann & Laszlo, 1991). Therefore,
the structural representations are meaning-based knowledge representations which are
changed and created to reflect the reconstruction of the theoretical and experimental
(Krajcik, Soloway, & Wu, 2000). Johnstone (1982) indicates that the macroscopic as
descriptive and functional, and sub-microscopic as representational and explanatory.
Chemistry has become a microscopic science (Hoffmann & Laszlo, 1991) and
microscopic representations are derived from the results of the macroscopic observable
phenomena.
According to Chittleborough (2004), symbolic representations are like metaphors where
real chemical phenomena are represented by symbols, equations, graphs, models,
pictures and analogies. In order to explain the real observable phenomenon, symbolic
representations are used. Sub-microscopic level explains the theoretical aspect of the
visible macroscopic phenomena. Changes in colour and formation of a precipitate
22
during an experiment is very much apparent and visually picked up. In the same
manner, the formation of certain gases, e.g., hydrogen sulphide, is smelt. The following
diagram illustrates examples at each level of chemical representation.
Figure 2.2: Examples of the three levels of representations used in Chemistry
Macroscopic
(experiments & experiences)
Sub-Microscopic Symbolic
(e.g., electrons, molecules, atoms ) (e.g., ball & stick models structural formulae, computer
models, equations)
Source: Chittleborough ( 2004: 19)
Certain facets of chemistry (e.g., chemical symbols) need rote learning to ensure long-
term memory retention, which does not necessarily facilitate conceptual understanding
of the material.
Research suggests that there is a dire need to emphasise the difficulty of transferring
between different types of representations within each level, as well as transferring from
one level to another (Treagust & Chittleborough, 2001).
23
2.3 THEORETICAL AND CONCEPTUAL FRAME WORK A framework within a research is a tool intended to assist a researcher to develop
awareness and understanding of the situation under scrutiny and to communicate
(Smyth, 2004). The researcher needs to prepare a framework for both the theoretical as
well as conceptual facet in order to explain the different methods and strategies that
he/she uses to conduct the research. The theoretical framework of the study is a
structure that can hold or support a theory of a research work and it presents the theory
which explains why the problem under study exists (Kozma & Khan, 2010). The
researcher formulates the theoretical framework based on his/her area of specialization,
which is in this case is chemistry. On the other hand, conceptual framework is a set of
broad ideas and principles taken from relevant fields of enquiry and used to structure a
subsequent presentation (Reichel & Ramey, 1987). The theoretical framework
presented within this research is based on the philosophy of constructivism.
The underlying aim of this research study was to investigate the conceptual
understanding of grade 12 learners’ on the chemical representations that form part of
the conceptual frame work. Various theories such as Piaget’s cognitive (personal)
constructivism, Vygotsky’s Zone of proximal development (ZPD), and the More
Knowledgeable Other (MKO), and conceptual change theory, were researched,
analysed and formed the basis of the research study.
2.3.1 Piaget and constructivism Knowledge is attained within a learners’ mind through interaction with the environment.
Piaget’s theory of constructivism stresses that children and adults use mental patterns
(schemes) to guide cognition (learning), and interpret new experiences or materials in
relation to existing schemes (Piaget, 1978). Bodner (1986) analyses Piaget’s theory of
knowledge creation and forwarded two key concepts, namely, assimilation and
accommodation. Assimilation is the process whereby a new experience / learning fit into
the old experience / learning. When a learner encounters situations in which existing
24
schemes cannot explain new information, existing schemes must be changed or new
ones made to enable the translation of information. Piaget refers to the process of
altering existing schemes, as accommodation.
Constructivists have firm convictions in the process of learning and the context in which
the learning takes place. They believe that there is a real world that learners
experience, but that meaning is imposed on the world by the learners, rather than
existing in the world independently of them. They also believe that there are many ways
to structure the world and there are many meanings or perspectives for any event or
concept (Duffy & Jonassen, 1991). In other words, for conceptual understanding to take
place such as in chemistry, learners need to experience different forms of
representation of a concept. Driscoll (1994) elaborates further on this by discussing how
learners need to access to multiple modes of representation. He maintains that when
learners revisit the same topic in rearranged contexts and from different conceptual
perspectives it encourages better understanding and learning. Constructivists believe
that in order to achieve complete understanding, the learner must examine the material
from multiple perspectives. If this is not done, the learner will achieve only a partial
understanding of the material. Multiple modes of representation allow the learner to
view the same content through different sensory modes.
2.3.2 Vygotsky and Social Constructivism Vygotsky, the pioneer of social constructivism, focused on the relationship between the
individual and society and the influence of social interaction, language and culture in
learning. His theory of social constructivism is also known as socio-cultural theory.
Under this concept, he has developed two theories: the Zone of proximal development
(ZPD) and the More Knowledgeable Other (MKO). According to Vygotsky (1978),
learning is a continual movement from the current intellectual level to a higher potential
intellectual level. Every function in the child’s growth appears twice: first, on the social
level and later, on the individual level; first, between people (inter-psychological) and
25
then inside the child (intra-psychological). This applies equally to voluntary attention, to
logical memory, and to the creation of concepts. All the other functions originate as
actual relationship between individuals (Vygotsky, 1978).
A child learns from an adult and reaches a stage whereby he / she will be able to do the
task without assistance. This was Vygotsky’s motivation to develop the theory, the zone
of proximal development. ZPD has been defined as “the distance between the actual
developmental level as determined by independent problem solving and the level of
potential development as determined through problem solving under adult guidance, or
in collaboration with more capable peers” (Vygotsky, 1978: 86). Vygotsky’s view is that
once a learner is within the ZPD for a particular task, providing appropriate assistance
(scaffolding) will assist the learner to achieve the task and once the learner masters the
task, the scaffolding can be removed and the learner then will be able to complete the
task again on his own. The MKO is considered to be the more knowledgeable person
than the learner. The MKO can be a teacher or peer who is more knowledgeable than
the learner on the relevant subject matter. Within the context of my study, the physical
sciences teacher is considered the MKO, who will facilitate the learning at the three
levels of chemical representation.
2.4 CONCEPTUAL UNDERSTANDING IN CHEMISTRY Conceptual understanding is the ability to use knowledge flexibly, to apply what is
learned and understood from one situation appropriately to another. It transcends far
above the common practice of following a procedure. It is meaningful learning and
involves retention and transfer of knowledge (Mayer, 2002). Learning, without
understanding the concepts is meaningless. Conceptual knowledge includes schemas
and mental models that represent how particular subject matter is organized and
structured, how the different parts or bits of information are interconnected and
interrelated in a more systematic manner and how these parts function together
(Anderson et al., 2001).
26
2.4.1 Conceptual nature of chemistry as a discipline Chemistry, by its very nature, is highly conceptual. Chemistry curricula commonly
incorporate many abstract concepts, which are central to further learning in both
chemistry and other sciences (Taber, 2002). These abstract concepts are important
because further chemistry concepts or theories cannot be easily understood if these
underpinning concepts are not sufficiently grasped by the student (Coll & Treagust,
2001; Nakhleh, 1992; Zoller, 1990). Chemistry learning entails the knowledge of the
three levels of representation and their relationship. Sanger, Phelps & Fienhold, (2000)
state that when relationships are formed between the three levels of representations,
learners understand the concepts and better learning takes place in chemistry.
Within the South African context, learners are exposed to chemistry, in the form of
chemical symbols, formulae and reactions as early as grade 8. However, many of these
learners are unable to interpret or express the correct equations when they reach grade
12. Most learners consider chemistry as being almost impossible to master, and this
may be the direct result of improper teaching and learning techniques utilised by
teachers. The teaching and understanding of chemistry is a challenge. Jonassen (1994)
indicate that many learners are unable to solve conceptual questions as they focus on
surface features of the problems and try to apply procedures. Research point to
learners having difficulties in chemistry learning as a result of the nature of the discipline
(Johnstone, 1984) and this is now further elaborated upon.
2.4.2 Difficulties in chemistry learning
Most learners have a conception that chemistry is very difficult to learn. The difficulties
of learning chemistry are related to the nature of chemistry itself and the methods by
which chemistry is customarily taught (Hussein & Reid, 2009). This problem of learners
performing badly in chemistry is not isolated only to South Africa, but is prevalent
throughout the world. Chemistry is generally regarded as a difficult subject. Johnstone
(1984), reports that the most difficult topics in chemistry, in view of learners, are the
27
mole, chemical formulae, and equations, and in organic chemistry, condensation and
hydrolysis. Chemistry curricula commonly incorporate many abstract concepts which
are central to further learning in both chemistry and other sciences (Taber, 2002).
These abstract concepts make the subject difficult for learners to learn and these
chemistry concepts are not sufficiently grasped by the learner (Ayas & Demirbas, 1997;
Coll & Treagust, 2001; Nakhleh, 1992; Nicoll, 2001; Sirhan, 2006; Zoller, 1990).
Prior knowledge or existing knowledge plays an important role in the process of any
learning according to constructivism. Often this knowledge comprises ideas which are
not in agreement with those generally accepted by scientists and these are named as
misconceptions (Garnett, & Hackling, 1995). These misconceptions are very difficult to
replace with concepts generally accepted as common scientific belief (Novak, & Gowin,
1984). Many researchers have shown that learners develop these conceptions from
various sources such as personal experiences, media, language, symbolic
representation, laboratory work etc (Chiu, 2005). According to Sanger and Badger
(2001), the characteristics of misconceptions are as follows: they are resistant to
change, persistent and embedded in an individual’s cognitive ecology and difficult to
extinguish even with instruction designed to address them. Since learning is the result
of interaction between what the learner is taught and his/her current ideas or
conceptions, misconceptions interfere with further learning (Canpolat et al., 2006).
These misconceptions make it difficult for the learners to see the link between the
science concepts and principles and eventually minimize the effective learning that
takes place. In order to eliminate misconceptions, a conceptual change needs to occur.
Researchers show that one of the essential characteristics of chemistry is the constant
interplay between the macroscopic, microscopic levels and symbolic levels of thought,
and it is this aspect of chemistry learning that represents a significant challenge to
novice learners (Bradley & Brand, 1985). The study of difficulty making connection
between the macroscopic world of observation and microscopic world of atoms and
molecules has a rather long tradition (Onwu & Randall, 2006; Treagust, Chittleborough
& Mamiala, 2003). Johnstone (1991) formulates that most chemistry instruction in high
28
school and college chemistry courses take place at the symbolic level and learners do
not understand the relationship between the symbolic and the other two levels. Learners
struggle to interpret a chemical reaction to the microscopic level. They are unable to
explain even the simplest chemical reactions in terms of particle level instead, many
memorize what is being presented on the symbolic level in terms of chemical equations
and mathematical relationships (Gabel, 2005).
The language of chemistry makes learning difficult because the meanings of the same
words in chemistry are different from the language used in daily life (Herron, 1996;
Johnstone, 1984).
2.4.3 Conceptual understanding and language It is an accepted fact that the medium of instruction of learning and teaching of science
plays an important role in the learners’ conceptual understanding of the subject. South
Africa is a multilingual country with eleven official languages. Most South African
learners learn physical sciences at school in a language medium (English), which is not
their home language. Learners’ level of conceptual understanding is negatively affected
when they are taught the subject using a language that is different from their home
language. Therefore, they find it difficult to understand the concepts in chemistry and
this implies poor performance in the subject. If learner’s access to science knowledge is
denied through inadequate communication and comprehension skills, then poor
conceptual understanding is inevitable and has disastrous consequences (Howie,
Scherman & Venter, 2008). English is a foreign language for many learners in this
country but it is their medium of instruction. The following is a narration of the learning
difficulty experienced by a learner, Kagiso, who is a science learner and a research
participant in the study conducted by Mji and Makgato (2006). Kagiso said, “All these
things are abstract like speed, velocity, acceleration…how can you see a
difference?….speed is speed. It is moving fast”. Kagiso associates speed with moving
fast - an English definition (Mji & Makgato, 2006 : 261).
29
The Language-in Education policy (LiEP) of 1997 (Department of Education, 1997),
gives permission to each school to decide on their own language of learning and
teaching (LoLT). But the School Governing Bodies (SGB) in townships and rural
communities think that their children should learn the subjects in English in order to
safeguard a bright future. Probyn et al. (2002) confirms this by saying that their
language policies appear to have been driven by the perception that English provides
access to education and economic success. By considering the growing demand of the
English language in the science and technological field, Rollnick (2000) also confirms
english is considered indispensable for communication internationally, especially as a
means to explain scientific concepts clearly. Johnstone and Sepelang (2001) conducted
studies on the effectiveness of teaching science in second language and concluded that
learners struggling to learn science in a second language lose at least 20 percent of
their capacity to reason and understand in the process. Vygotsky (1978) claims that
concepts cannot be acquired in conscious form without language and a learner cannot
have a conscious understanding of concepts before they are explained in a related
context using a language.
Teachers often switch from English to the learners’ home language to explain new
concepts, to clarify statements or questions, to emphasise points, to make connections
with learners’ own contexts and experiences (Probyn, 2003). This creates tremendous
problems for the learners with regard to being able to engage with the curriculum.
According to Cumins (2000) bridging the gap and acquiring not only proficiency in
English but also the kind of cognitive academic language proficiency becomes
impossible for learners if they are taught in a second language. Research conducted by
Howie (2001) points to learners who study mathematics and science in their second
language tends to have difficulty articulating their answers to open-ended questions and
have trouble understanding several of the questions. Danili and Reid (2004) indicates
that if learners study chemistry in a language other than their mother tongue, difficulties
experienced in chemical language could be linguistic, contextual or cultural in nature.
30
The UMALUSI team which was involved in evaluation of 2008 NSC question papers
found the language levels in the paper too high, the paper was too wordy meaning that
there was too much text and too many difficult words for the average South African
learner (Overview, 2009). These questions generally entail a learner to have a higher
degree of interpretation skills which essentially becomes too much for a South African
learner whose second language is English.
Research conducted in Malaysia where science is taught in English, which is their
second language, proved that with the appropriate methodology and sensitivity, content
and language integrated learning (CLIL) can be done by the content specialist (Ibrahim,
Gill, Nambiar, & Hua, 2009).The constructivist theory that allows lecturers to optimize
input and simultaneously raise the content schema of the students through an active
teaching style will raise the quality of the teaching-learning context. Ver Beek and
Louters (1991) conducted studies on the problems in understanding the chemical
language and recommended the following:
• Learners’ exposure to chemical language need to be maximized;
• Teachers should not assume that learners are familiar with chemical terms and
these terms should be introduced carefully.
2.5 CHEMISTRY TEACHING As a result of the complex nature of chemistry, this subject is regarded as one of the
most difficult to teach (Childs & Sheehan, 2009; Gabel, 1999). Often it is the teaching
approach that is used by teachers that contributes to learning difficulties encountered by
learners. For example, teachers teach the symbols of elements to learners by indicating
to them that the first letter of the name of the element becomes the symbol of the
element which should be represented in capital form (e.g., H for hydrogen). However in
the case of elements whose symbols are originated from their Latin names (e.g., Na for
sodium), this technique often fails as many learners associate S for sodium instead of
Na.
31
Johnstone (1991) believes that chemistry can be easily taught when presented in the
three forms of representation. However, teachers have to use appropriate teaching
strategies to make this presentation easy for the learners. The sub-microscopic level of
chemistry deals with the properties of matter, such as atoms and molecules.
Explanations of the macroscopic level of chemistry is done at the sub-microscopic level,
where the behaviour of substances is interpreted in terms of the unseen and molecular
and recorded in some representational language and notation at symbolic level
(Johnstone, 2000).
2.5.1 Pedagogical Content Knowledge in Science Much research has been conducted on teaching chemistry in recent years such as: the
development of the PCK (Van Driel, 2001); the factors which hinder or promote the
development of PCK (Grossner, 1990; Veal & MaKinster, 1998); instructors attitude
towards active learning (Pundak & Herscovitz, 2009); and teachers’ pedagogical
knowledge and teaching higher order thinking skills. These studies inspect the
relationship between the pedagogical content knowledge of educators’ and teaching
strategies used. Van Driel & Graber (2002) highlight the two following elements as
central in any conceptualization of PCK:
• Knowledge of representation of subject matter, instructional strategies and
incorporating these representations.
• Understanding of specific student conceptions and learning difficulties.
Therefore, it is evident that “these elements are interwind and should be used in a
flexible manner: the new representations and strategies teachers have at their disposal
within a certain domain, and the better they can teach in this domain.PCK referes to
particular topics and it is to be discerned from knowledge of pedagogy, of educational
purposes, and of learner characteristics in a general sense” (van Driel, De Jong &
Verloop, 2000: 573-574).
32
2.5.2 Learner Centred Teaching The current education system of South Africa follows a learner-centred curriculum. In
the learner-centred classroom, the emphasis is placed on the person who is doing the
learning (Weimer, 2002). The paradigm shift away from teaching to an emphasis on
learning has encouraged power to be moved from the teacher to the learner (Barr, &
Tagg, 1995). According to Brandes & Ginnis (1996:12-26), the main principles of learner
centred teaching, are:
• The learner is responsible for her / his learning development.
• Involvement and participation are necessary for learning.
• The relationship between learners is equal, promoting growth and
development.
• The teacher becomes a facilitator and resource person.
• The learner experiences confluence in his education (affective and cognitive
domains flow together).
It is envisaged that the above principles of learning will be reflected in a chemistry class.
2.5.3 Conceptual Change Perspective to Teaching From a constructivist perspective, learning is an individual process that involves linking
new ideas and experiences with what the learner already knows (Gabel & Liang, 2005).
According to Ausubel, (1968) the most important factor that influence learning is what
the learner already knows. Based on this constructivist perspective, Posner, Strike,
Hewson & Gertzog (1982) developed the conceptual change model (CCM) which
suggests that learning occurs when the learner recognizes a need and becomes
dissatisfied with his / her existing ideas, thus new ideas appear intelligible, plausible and
fruitful. Many conceptual change teaching approaches have been developed and have
positive effects in promoting learners’ conceptual understanding of science as well as in
improving learners’ attitude towards science learning (Hand & Treagust, 1991). Based
33
on their research, Posner et al., (1982: 225) make the following recommendations in
effecting conceptual change in learners:
• Develop lectures, demonstrations, problems, and labs which can be used to
create cognitive conflicts in students.
• Organize instruction so that teachers can spend a substantial portion of their time
in diagnosing errors in student thinking and identifying defensive moves used by
students to resist accommodation.
• Develop the kinds of strategies which teachers could include in their repertoire to
deal with student errors and moves that interfere with accommodation.
• Help learners make sense of science content by representing content in multiple
modes (e.g., verbal, mathematical, concrete-practical, pictorial), and by helping
learners translate from one mode of representation to another (Clement, 1977)
• Develop evaluation techniques to help the teacher track the process of
conceptual change in students (e.g., the Piagetian clinical interview).
2.5.4 Problem Solving Approach and Teaching Research within the science education discipline has often focused on the problem
solving ability and conceptual understanding of chemistry learners. Problem solving is a
commonly used teaching method in chemistry because it challenges learners’
understanding of the subject matter and requires them to apply the concepts that they
have learned (Gabel & Bunce, 1994). Learners’ achievement in science at the
secondary school level depends on their proficiency in solving algorithmic and
conceptual problems. To solve conceptual problems learners need a sound
understanding of chemical concepts while algorithmic problems require the application
and the manipulation of certain mathematical concepts and formulae. Even without any
understanding of concepts in chemistry, some learners can solve problems easily.
Learners can master skills of applying and manipulating science formulae without
acquiring conceptual understanding of chemistry (BouJaoude 2004) leading them to
solve without necessarily understanding underlying scientific concepts (Heyworth,
1999).
34
Science teachers assume that algorithmic problem-solving will automatically lead to
conceptual understanding. Researches show that lack of conceptual understanding,
might be due to the prevalence of algorithmic problem solving in class room evaluation
practices (Nakhleh 1992) and hinders the learning of further science concepts
(Pickering, 1990), and may even lead to misconceptions. Since success in solving
conceptual problems requires sound understanding of underlying concepts, it can be
assumed that learners who possess alternative conceptions would perform poorly in
such problems (BouJaoude, 2004).
Problem solving strategies illustrate several steps to follow. Hanson and Wolfskill
(2000), identifies these steps as evaluating the data given, planning a solution,
executing the plan, validating the solution and assessing the solution. RamsDen (1995)
identifies two approaches to learning, namely the surface approach and a deep
approach. The deep approach involves an intention to understand and a surface
approach describes the intention to reproduce (Entwistle & Waterson 1998). Learners
with a deep approach to learning are called meaningful learners while learners with a
surface approach are labelled as rote learners (BouJaoude, 2004). Learners who learn
by the method of rote learning find it very difficult to transfer information from the
macroscopic level to microscopic level of understanding (Staver & Lumpe, 1995).
Rote may create a dislike towards chemistry learning. Nakhleh (1992) warns that this
may lead to aversion from chemistry and is problematic, especially if the goal is for
learners to use chemistry to address everyday problems and to pursue higher studies in
chemistry. As an example, the activity series of metals is explained as follows;
Mg(s) + Cu+ (aq) → Mg2+
(aq) + Cu(s).
Using this example, one can predict other reactions related to the activity series. It
however doesn’t indicate that by purely memorizing the theory, a learner can apply this
knowledge in solving problems at other situations. This would require a complete
understanding on oxidation – reduction reaction which means that learners should be
able to interchange between sub-microscopic and symbolic levels of representation.
The reaction between magnesium metal and copper sulphate solution can be explained
35
as follows. Teachers have to teach learners about the oxidation number of magnesium
and copper and copper atoms, the conversion of atoms into ions and ions into atoms
using oxidation and reduction half-reaction equations. Magnesium oxidises because it is
more reactive than copper. Copper ions receive electrons from magnesium atom and
become copper atoms. During this process the blue colour of the solution gradually
disappears. The net reaction is represented symbolically using the following equations,
Mg(s) → Mg2+(aq) + 2e- (oxidation half- reaction)
Cu2+(aq) + 2e- → Cu(s) (reduction half- reaction)
Mg(s) + Cu+ (aq) → Mg(aq)
2+ + Cu(s).
The above reaction is a typical example to explain the transformation of the different
levels of chemical representations (macroscopic level ↔ sub-microscopic level ↔
symbolic level). It is therefore imperative that teachers use different strategies such as
models, diagrams, explanations, etc that can enhance the problem solving abilities of
learners.
2.5.5 Cooperative Learning as a Teaching Strategy Cooperative learning promotes working in groups. Cooperative learning is grounded in
the belief that learning is most effective when learners are involved in sharing ideas and
work cooperatively to complete academic tasks (Zakaria & Iksan, 2007). Successful
cooperative and collaborative learning experiences in the classroom require that
teachers attend to the formation of the groups, the composition of the groups, the
dynamics of the groups, the assessment of the learner work and the design of the group
task (Ventigmiglia, 1994).
Johnson, Johnson and Smith, (1998: 7) state that cooperative learning promotes,
• Positive interdependence where the team members perceive that they need each
other in order to complete the group’s task. The success of one learner is
dependent on the success of the other.
36
• Face - to - Face Promotive Interaction, whereby team members promote each
other’s productivity by helping, sharing, and encouraging efforts to produce.
Members explain, discuss, and teach what they know to teammates,
• Individual accountability, where the quality and quantity of each learner’s
contributions is assessed and the results are given to the group and the
individual,
• Group Processing, where the group discuss how well they are achieving their
goals and maintaining effective working relationships among members,
• The development of interpersonal and small group skills.
In groups, learners can do active learning in problem solving, practical work and other
activities. In the NCS curriculum of physical sciences, as part of continuous assessment
(CASS), learners have to perform two practical investigations where they have to work
in groups. During this process, the task is divided into several parts and each learner is
assigned with one part to do. If each learner does not satisfactorily carry out the
assigned task, then the group effort is compromised. In view of this it is very important
that science teachers should try to adopt cooperative learning as a teaching strategy to
enhance conceptual learning and to promote scientific skills. There may be certain
challenges that teachers face, such as, the extra preparation time needed, preparation
of extra resources for the groups, a fear of loss of content coverage, and learners who
may be lacking in knowledge of working in groups (Zakaria & Iksan, 2007).
2.5.6 Practical / Laboratory work as a Teaching Strategy Practical work is an indispensable part of teaching and learning science especially in
chemistry (Gallagher, 1987). Various reasons have been advanced for adopting a
pedagogy based on practical work. Firstly, practical work can facilitate the
understanding of concepts in science. As mentioned already, chemistry involves
complex and abstract subject matter, and through practical work these concepts can
become more concrete to learners (Hodson, 1993). Secondly, practical work enables
37
learners to develop experimental skills (Woolnough & Allsop, 1985), for example the
manipulation of a burette in doing a titration. Thirdly, practical work gives learners an
insight in to the world of the scientist and the nature of science (Roth, 1995) and the
opportunity for learners to act like a real scientist by engaging the learners in the
scientific method (Bruner, 1986). Finally, practical work is highly motivational and
stimulates interest in the learning of science (Woolnough & Allsop, 1985).
In particular with regard to chemistry learning, laboratory experiences enable
conceptual understanding at the macroscopic level that can stimulate engagement at
the sub-microscopic and symbolic levels.
2.6 THE NATIONAL GRADE 12 EXAMINATION The aim of my study was to investigate the conceptual understanding of chemical
representations by grade 12 learners. The first objective was to determine the
performance of grade 12 learners in a national external examination responding to
questions at the macroscopic, sub-microscopic and symbolic levels of chemical
representation. In order to contextualise the study I now present an overview of this
examination and assessment in physical sciences.
General and Further Education and Training Quality Assurance Council (UMALUSI) is
the statutory organization which sets and monitors standards for General and Further
education and training in South Africa with the purpose of continually enhancing the
quality of education and training (SA Year book, 2009/2010). The NCS curriculum
embodies the skills, values and knowledge envisaged by the SA Constitution.
2.6.1 Assessment in the grade 12 NSC examination NSC examination comprises of two parts:
• external examination which contributes 75% of the learners’ promotion mark and
• School Based Assessment (SBA) which forms 25% of the final promotion mark.
38
The weighting of the cognitive levels of the chemistry (paper 2) is given below in Table
2.1
Table 2.1 Weighting of Cognitive Levels
Cognitive Level Description
Weighting
Recall (Knowledge) 15 Comprehension 40 Analysis, Application 35 Evaluation, Synthesis 10
Source: Subject Assessment Guidelines Physical sciences: January 2008
The grade 12 content is assessed through the physical sciences Learning Outcomes
(LO). The weighting and interpretation of learning outcomes are outlined in the Table
below.
Table 2.2: Weighting of learning outcomes
Learning outcome Weighting
LO 1 Practical scientific enquiry and problem-solving skills
30 – 40%
LO 2 Constructing and applying scientific knowledge 50 – 60%
LO 3 The nature of science and its relationship to technology, society and the environment
5 – 15%
Source: Subject Assessment Guidelines Physical sciences: January 2008 All skills and application of knowledge learnt in grades 10 and 11 are transferable and
applicable to assessment in grade 12 in particular, skills and knowledge from grades 10
and 11 that may be assessed in grade 12 include the following:
• stoichiometric calculations
• concentration calculations
• balancing of chemical equations
39
• use of oxidation numbers
• identification and description of intermolecular forces (Van der Waal's forces
and hydrogen bonds)
• acids and bases
The themes included in the P2: chemistry examination was included in chapter 1.The
following format of mark allocation was used for the final grade 12 examination in 2008.
Table 2.3: Mark allocation of question paper, P2: Chemistry
Knowledge Area Theme Marks Matter and materials (±33%)
Organic molecules ± 50
Chemical change (±50%)
Energy and chemical change Grade 11 Rate and extent of reaction ± 75 Electrochemical reactions
Chemical systems (±17%)
Chloroalkali industry Fertiliser industry Batteries
±25
Total 150 Source: Subject Assessment Guidelines Physical sciences: January 2008 The chemistry question paper for 2008 was divided into two sections, section A and
section B. Section A contained one word answers, matching items, true-false items, and
multiple choice items. Section B contained long questions and assessed all three
themes in chemistry. The following format was be used for the final Grade 12
examination in 2008.
Table 2.4: Format of grade 12 NSC P2 Chemistry
Paper 2: Chemistry (3 hours ) Marks SECTION A: One-word answers 5 Matching items 5 False items 10 Multiple-choice questions 15
40
SECTION B: Longer questions assessing all themes
115
Total 150
Source: Physical sciences exam guide line: 2008
2.6.2 Learner attainment in physical sciences In the new curriculum, according to the performance, the learners are placed in different
levels, from level 1-7, 1, being the lowest level (fail) of achievement and 7 being an
outstanding achievement. These levels are described in Table 2.5 below.
Table 2.5: Learner Achievement Level
Subject Assessment Guidelines Physical sciences: January 2008
Achievement
Level
Level descriptor (Rating) Marks %
7 Outstanding achievement 80 – 100
6 Meritorious achievement 70 –79
5 Substantial achievement 60 – 69
4 Adequate achievement 50 – 59
3 Moderate achievement 40 – 49
2 Elementary achievement 30 – 39
1 Not achieved 0 – 29
By the end of grade 12, the learner with outstanding achievement (level 7) can:
• Apply scientific knowledge in everyday contexts, analyse and evaluate
scientific knowledge and indigenous knowledge systems claiming by
indicating the correlation among them and explain the acceptance of
different claims.
41
• Formulate a scientific investigative problem when presented with a
complex scenario and develop and apply own criteria to analyse and
evaluate problem solving processes and solutions generated.
• Evaluate findings, select and use appropriate terminology to condense
information, present it in a composite report according to prescribed
criteria and adapt the report for different purposes and different
audiences.
• Evaluate different perspectives and suggest a justifiable decision
regarding the application of specific technology, its scientific nature and
its ability to explain phenomena, events and occurrences.
• Assess South Africa’s contribution to management, utilization and
development of resources and the environment to ensure global
sustainability (GDE, 2005).
2.7 CLASSIFYING QUESTIONS IN THE 2008 NCS CHEMISTRY
EXAMINATION PAPER INTO LEVELS OF CHEMICAL REPRESENTATION Classification can be defined as the basic cognitive task of arranging concepts into
classes or categories (Stains and Talanquer, 2007). Classification plays a central role in
chemistry, where it is used not only as a way to organize knowledge but also as a
powerful predictive tool (Schummer, 1998). Scientists rely on classifications generally to
conclude the results of their research. Chemists rely heavily on classification systems in
their everyday work. The diverse classification systems used in chemistry to make
predictions and build explanations are based on the identification of features at different
levels of representation; macroscopic, microscopic, and symbolic (Gabel, 1999;
Johnstone, 1993). Research reveals that learners struggle to understand concepts like
the particulate nature of matter, and the mole. A lack of deep conceptual understanding
of chemistry prevents learners from coming up with a well propounded solutions to
42
quantitative problems (Gabel, Briner, & Haines, 1992; Gabel, 1993; Garnett, Garnett, &
Hackling, 1995; Noh & Scharmann, 1997).
The grade 12 NSC question paper is a combination of both qualitative and quantitative
type of questions. The quantitative aspect of chemistry deals with the amount of
substances present while the qualitative chemistry deals with what type of substances
are present in a chemical reaction. The main aim of this study is to analyse the grade 12
learners’ levels of conceptual understanding of chemical representations. Generally,
learner performance in an examination or test can be regarded as a direct measure of
their conceptual understanding of the subject. Learners’ written answers reveal their
conceptual knowledge of the subject. In the present research, the grade 12 examination
questions were classified at different levels of representation in order to study learner
performance at each level.
In the formulation of this framework, I looked into the relationship of each question with
the three levels of chemical representation. Some questions belong to macroscopic
level only, some to sub-microscopic and some to symbolic. In some cases,
transformation from one level to another and vice versa (eg: macroscopic ↔ symbolic)
occurs. Based on this, I developed a Classification Frame work of Chemical
Representation (CFCR). The grade 12 NSC chemistry questions of 2008 were classified
into seven categories,
• Macroscopic level - This level deals with the observable part of a chemical
reaction where changes can be observed, felt, and smelled. An example of a
question of this category is as follows: What do you observe when magnesium
burns in oxygen?
• Sub-microscopic level - This is also the real part of chemistry but explanations
are abstract. Whatever happens at the macroscopic level is explained at this
level. This level of chemistry deals with the particulate nature of matter. For
example, learners may be asked to explain the chemical changes that take place
in the burning of magnesium with oxygen.
43
• Symbolic level - This level represents the matter in terms of symbols, formulae,
and equations. Here the task may be for learners to write a chemical equation of
the reaction described above. According to Dori et al. (2002) learners often
experience difficulties at this level. For example, such difficulties include (1)
understanding the two different meanings in the symbol 2Ag2O, and (2) deciding
when a symbol represents a mole of atoms (Cl) and when it stands for a mole of
molecules (Cl2).
• Macroscopic ↔ sub-microscopic level transformation- In this case, learners
should know the transformation that takes place from the macroscopic level to
the sub-microscopic level. For example, learners may be asked to burn a piece
of magnesium ribbon in oxygen gas and explain the chemical changes that take
place for magnesium and oxygen gas. At the macroscopic level learners may
observe magnesium ribbon burns with bright flame forming a greyish ash. This
transformation may be explained at the sub – microscopic level as follows.
Magnesium atom changes into magnesium ion by donating two electrons to the
oxygen atom. The oxygen atom changes into oxide ions. The two ions combine
to form magnesium oxide, which appears as the greyish ash.
• Macroscopic ↔ symbolic level transformation – Learners need to be able to
translate what they observe during a chemical reaction into symbolic language.
This can be also explained using the above example. Learners may be asked to
burn a piece of magnesium ribbon in oxygen gas and explain this reaction using
a chemical equation by specifying the phases of the reactants and products. At
the macroscopic level learners may observe magnesium ribbon burns with bright
flame forming a greyish ash. This reaction at the macroscopic level can be
represented at the symbolic level using the equation for the reaction.
2Mg(s) + O2(g) → 2MgO(s)
• Sub-microscopic ↔ symbolic level transformation – Some questions relate to the
transformation from the sub-microscopic level to the symbolic level and vice
verse. The explanation of dissolution process of sodium chloride in water can be
44
expressed using chemical language of symbols, for example when sodium
chloride dissolves in water, it ionizes to sodium ions and chloride ions and can be
represented in symbolic form as:
NaCl (aq) → Na+ (aq) + Cl-(aq).
• Macroscopic ↔ sub-microscopic ↔ symbolic level transformation – This
transformation is from macroscopic to sub-microscopic to symbolic and vice
versa. In this transformation, all three levels are involved. When all three levels of
representation are involved, another type of difficulty may arise for some learners
i.e., making connections among the three levels of representation (Kozma,
2000).
• As an example, learners may be asked to explain (by giving all details), what
happens when a piece of magnesium ribbon burns in oxygen. To answer this
question, a learner should describe his/her observations, know the particulate
nature of matter (in this case), and then be able to transform the above
information using symbols and equations. A sample of explanations is given
below:
At the macroscopic level- Magnesium burns in oxygen gas with a very bright
flame and a greyish ash is formed;
At the sub-microscopic level – During the burning, magnesium atom changes
to magnesium ions ( positively charged) and oxygen molecule changes into
negatively charged oxide ions;
At the symbolic level – Mg(s) + O2 (g) → MgO(s)
By using the Classification Framework of Chemical Representation (CFCR), the NSC
chemistry questions of 2008 were classified and marks were recorded in order to study
the learner performance qualitatively.
45
2.8 CONCLUSION In this chapter I presented an extensive review of literature on the chemical
representations of matter and the learning of chemistry in relation to chemical
representations. I also discussed theories that inform chemistry learning and also
explored the implications of these theories for chemistry teaching and learning. The
teaching strategies and principles suitable to inculcate conceptual understanding such
as cooperative learning, learner-centred teaching, problem solving approach and
teaching, and practical work as a teaching strategy were also explained and discussed.
I highlighted difficulties learners experience in chemistry learning in view of the poor
examination results. I described the current NSC chemistry examination system in detail
and then introduced the classification framework that was used in the analysis of the
chemistry examination paper and scripts.
46
CHAPTER THREE
3. RESEARCH DESIGN AND METHODOLOGY
3.1 INTRODUCTION This research study aimed to investigate the conceptual understanding of chemical
representations by learners in grade 12. The performance of learners in questions at
the various levels of chemical representation is an indication of their conceptual
understanding at these levels. However, for high levels of attainment, learners must
have an in- depth understanding and knowledge of the content as well as a conceptual
understanding of fundamental concepts (Potgieter, 2011). “But the abstract nature of
sub-microscopic representations and symbolic representations make it difficult for
learners to connect them with macroscopic phenomena” (Griffith & Preston, 1992:1).
However, the level of understanding of these representations by learners depends on
the strategies that are used by teachers to facilitate the unfolding of these concepts to
the learners. Therefore, this research study also aimed to investigate and describe how
teachers facilitate the learner’s conceptual understanding at the macroscopic, sub-
microscopic and symbolic levels of chemical representation. In this chapter, the
research design and methodology are discussed as well as the terms that are
associated with this research methodology are explained.
3.2 RESEARCH QUESTIONS AND OBJECTIVES The specific research questions that guided the study are:
1. What is the performance of grade 12 learners in responding to questions at the
macroscopic, sub-microscopic and symbolic levels of chemical representation as
demanded in a high stakes chemistry examination?
2. What strategies do teachers use in facilitating learner understanding at the
macroscopic, sub-microscopic and symbolic levels of chemical representation?
47
Accordingly, the following objectives were set:
1. To determine the performance of grade 12 learners in responding to questions at the
macroscopic, sub-microscopic and symbolic levels of chemical representation.
2. To describe how teachers facilitate learner conceptual understanding at the
macroscopic, sub-microscopic and symbolic levels of chemical representation.
3.3 RESEARCH DESIGN AND METHODOLOGY A research design includes all the plans and procedures used to conduct the research.
Thyer (1993) views a research design as a blue print/detailed plan for how a research
study is to be conducted. Hysamen (1993) further explains that this plan/blueprint offers
the framework according to which data is to be collected to investigate the research
question in the most economical manner. However, research methods are more specific
and they refer to the techniques that are used for data collection and analysis (Creswell,
2003). In this study both qualitative and quantitative research methodologies were
utilised for the collection and analysis of the data.
3.3.1 Quantitative Research Quantitative research deals with data that is principally numerical and emphasizes
measurements. Quantitative research is all about quantifying relationships between
variables. Variables are things like weight, performance, time and treatment. Hopkins
(2008) indicates that the relationships between variables are expressed using effect
statistics, such as correlations, relative frequencies, or differences between means. Two
types of strategies of inquiry are used in the quantitative research namely, surveys and
experiments. Survey research can be used to obtain a quantitative or numeric
description of patterns, attitudes, or opinion of a population by studying a sample of a
population (Creswell, 2009). It takes universal propositions and generalizations as a
point of departure (Schurink, 1998). A form of deductive reasoning is used in this type of
research. Quantitative data includes closed-ended information and the data analysis
consists of statistical analysis (Creswell & Plano Clarke, 2007). Many researchers view
48
quantitative research design as the best approach to scientific research because it
offers precise measurement and analysis. In quantitative research design the
researcher will count and classify, and build statistical models which is used to explain
what is observed. Data collected using this research approach is in the form of numbers
and statistics (Jenkins, 2009).
In this study, a quantitative research method was utilised in the first phase of data
collection and analysis, where 500 chemistry exam scripts from the 2008 NSC
examination from the Gauteng Province were collected and analysed to establish
learner performance in responding to questions at the macroscopic, microscopic and
symbolic levels of chemical representation.
3.3.2 Qualitative Research Qualitative analysis is used for in-depth inquiry and the data consists of open-ended
information that the researcher gathers through interviews with participants (Creswell &
Clarke, 2007). In a qualitative study the factors that affect the results are not controlled
because it is this freedom and the natural development of action and representation that
a researcher wishes to record (Henning et al., 2004). Qualitative researchers tend to
collect data in the field at the site where participants experience the issue or problem
under study. They collect data themselves through examining documents, observing
behaviour, or interviewing participants. The researchers gather multiple forms of data,
such as interviews, observation, and documents, rather than relying on a single data
source. Creswell (2009) indicates that, after collecting the data the researcher reviews
all of the data, makes sense of it, and organizes it into categories or themes that cut
across all of the data sources. Creswell (2009) further points out that qualitative
research is a form of interpretive inquiry in which researchers make an interpretation of
what they see and understand. Qualitative inquiry, which focuses on meaning in
context, requires a data collection instrument that is sensitive to underlying meaning
when gathering and interpreting data. According to Merriam (1998) activities such as
interviewing, observing, and analysing are central to qualitative research and humans
49
are well suited to execute this task. Therefore, interviews and observations are the best
form of data collection to describe how teachers facilitate learner’s conceptual
understanding at the macroscopic, sub-microscopic and symbolic levels of chemical
representation. Hence a qualitative research method was utilised in this study in the
second phase of the data collection and analysis of the data. Pre- interviews and class
observations of selected teachers were used to collect data at this stage.
3.4 PREPARATION OF THE TOOL FOR DATA COLLECTION Learner performance in any examination is a direct measure of their understanding of
the concepts or their conceptual understanding of the subject. Chemical concepts are
divided into three levels of chemical representations such as macroscopic, microscopic
and symbolic. In other words, conceptual understanding in chemistry means an
understanding of the three levels of representation. As I mentioned in chapter two, the
grade 12 NSC chemistry question paper is a combination of both qualitative and
quantitative type of questions.
Since the purpose of the research was to study the grade 12 learners’ conceptual
understanding of chemical representations, the data collection needed to be based on
the three levels of chemical representations. Hence, it was essential for me to prepare a
classification framework of chemical representations for the data collection. Some
questions belong to macroscopic level only, some to sub-microscopic and some to
symbolic. In some cases, transformation from one level to another and vice versa (eg:
macroscopic ↔ symbolic) occurs. The questions in the entire chemistry paper are
divided into seven categories: macroscopic level; sub-microscopic level; symbolic level;
macroscopic ↔ sub-microscopic level; macroscopic ↔ symbolic level; sub-microscopic
↔ symbolic level; and macroscopic ↔ sub-microscopic ↔ symbolic level.
• Macroscopic level- This level deals with the observable part of a chemical
reaction where changes can be observed, felt, and smelled.
50
• Sub- microscopic level- At this level, learners have to learn about the content part
that is abstract but real. This level of chemistry deals with the particulate nature
of matter.
• Symbolic level- Matter is represented in terms of symbols, formulae, and
equations.
• Macroscopic ↔ sub- microscopic level – Learners must know the transformation
from the macroscopic level to the sub-microscopic level.
• Macroscopic ↔ symbolic level – This is the transformation of the concept in the
macroscopic level to the symbolic level by using symbols.
• Sub-microscopic ↔ symbolic level- This level represents the transformation of
concept from the sub-microscopic level to symbolic level and vice versa.
• Macroscopic ↔ sub- microscopic ↔ symbolic level - This level represents the
transformation of the concept from the macroscopic to sub-microscopic to
symbolic level and vice versa.
Based on this, I developed a Classification Framework of Chemical Representation
(CFCR) as shown in table 3.1 below.
Table 3.1: Categorization of levels of representation in chemistry
M
acro
scop
ic
leve
l
Sub
-m
icro
scop
ic
leve
l
Sym
bolic
le
vel
mac
rosc
opic
↔
sub
- m
icro
scop
ic
leve
l
mac
rosc
opic
↔
sym
bolic
sub
– m
icro
scop
ic
↔
sym
bolic
mac
rosc
opic
↔
sub
- m
i cro
scop
ic
↔sy
mbo
lic
Question Question Question Question Question Question Question
e.g. 1.1 e.g. 1.3 e.g. 1.5
e.g. 2.4
e.g. 2.1
e.g. 5.6
e.g. 9.6.1
51
3.5 DATA COLLECTION Collecting data includes identifying and selecting individuals for a study, obtaining their
permission to be studied, and gathering information by administering instruments,
through asking them questions, or observing their behaviour (Creswell, 2002).
Five hundred learner scripts from the 2008 National Senior Certificate Examination from
the Gauteng Province were randomly selected by the Gauteng Department of Education
for the first part of the research study. These scripts were in the possession of the
University of Johannesburg for a research project undertaken by the university for which
I was a participant. These scripts were released with special permission from the
University of Johannesburg for my study. Since the scripts were selected randomly the
study had equal chances of representing learners from the previously disadvantaged
schools as well as from the former Model C schools. Learner marks were recorded
against each question. There were twelve main questions and seventy two sub
questions. The marks of each question as well as the sub questions were collected and
recorded against the relevant level of chemical representation. After recording and
classifying the marks as per the CFCR framework, the data was analysed using SPSS.
Pre- interviews and classroom observations were conducted to collect data for the
second part of the study which was the qualitative research. The purpose of this phase
of the research was to identify strategies that physical sciences teachers use in
facilitating learner conceptual understanding at the macroscopic, sub-microscopic and
symbolic levels of chemical representation. An interview schedule (Appendix, E) was
prepared and used to collect data during the pre- interviews. These questions were
open ended. All teachers were asked the same questions for uniformity. All three
interviews were audio-taped. After the interview, lesson observations were carried out
for the three teachers, lessons were audio-taped, video-taped and field notes were
taken. The lesson observation is defined by the following operational terms e.g.,
planning, introduction, presentation, practical demonstration, learners’ practical work,
group work, written work, home work, closure, and the criteria to the whole lesson.
52
Observation notes give an opportunity to get a full account of what has happened in the
classroom (De Vos, 1998).
Qualitative data consists of open ended information that the researcher gathers through
interviews with the participants. According to Keats (2000), the advantage of asking
open ended questions during the interviews allows the participants complete freedom to
reply and it does not suggest answers or offer alternatives. Three secondary school
physical science teachers from three previously disadvantaged schools were selected
to participate in the research study. Semi structured interviews were conducted with the
three participants (teachers). According to Kvale (1983) the purpose of the interview is
to describe the structure of the experience of the individual. According to Kvale
(1996:145), the quality criteria for an interview are as follows:
• The extent of spontaneous, rich, specific, and relevant answers from the
interviewee.
• The shorter the interviewer’s questions and the longer the interviewer’s answers,
the better.
• The degree to which the interviewer follows up and clarifies the meanings of the
relevant aspects of the answers.
• The ideal interview is to a large extent interpreted throughout the interview.
• The interviewer attempts to verify his or her interpretations of the subject’s
answers in the course of the interview.
• The interview is ‘self-communicating’ – it is a story contained in itself that hardly
requires much extra descriptions and explanations.
Classroom observations were also used to collect data for the second phase of the
study. Observation is a means of collecting data in qualitative research. It offers a
firsthand account of the situation under study and when combined with the data
collected through interviews and document analysis, it allows for a holistic interpretation
of the phenomenon being investigated (Merriam, 1988). Observation methods are used
by researchers in a variety of ways. They provide researchers with ways to check for
nonverbal expression of feelings, determine who interacts with whom, grasp how
53
participants communicate with each other, and check for how much time is spent on
various activities (Schmuck, 1997). Classroom observation can be used as a way to
increase the validity of the study as observations may help the researcher get a better
analysis, or surveys, questionnaires, or other more qualitative methods (Kawulich,
2005).
The three teachers who participated in the study were observed in practice at their own
schools. Hence a natural environment existed while they were conducting their lessons.
Classroom observation can be used to identify the current status of instructional
problems. The classroom observations were carried out without any participation of the
researcher. The data collected by the classroom observation will reveal more about
data acquired through the interviews. “An educational researcher wishes to find out how
classroom function with regard to teacher communication, and may draw up an
observation protocol or schedule in which he / she will focus on the teacher’s talk and
other forms of communication” (Henning, 2004:88).
3.6 SAMPLING Learner scripts for the first phase of research study, the quantitative inquiry, were
selected randomly and analysed. This type of sampling ensures that the possibility of
the inclusion of learners, from all types of schools, is equal. The phase two of the study
involved three physical sciences teachers from two secondary schools situated in
Orange farm in the Gauteng Province. Since the purpose of the study was an in-depth
analysis of learner performance, a combination of convenient and purposive sampling
(Warren, 2002) was chosen to identify the participants. The sampling was purposive in
that all three teachers were teaching grade 12 physical sciences, and this was important
as I wanted to investigate the strategies used by them in facilitating conceptual
understanding of grade 12 learners at the levels of chemical representation already
outlined. Furthermore, the sample was convenient as the schools where the teachers
taught were very accessible to me. The teachers were markers/senior markers of the
grade 12 NSC examination and have more than 10 years of teaching experience,
54
especially chemistry at grade 12 level. They all had the minimum qualifications required
to teach physical sciences up to grade 12 level. Mr Mashigo holds a secondary school
teachers diploma (STD) with physics and mathematics as majors, Mrs Khumalo has
B.Ed (Honours) in chemistry and life sciences as well as B.Ed (Honours) in education
management and Mrs Mbele has a secondary school teacher diploma (STD) with
chemistry and life sciences as majors as well as a further diploma (FDE) and B.Ed in
education management. The two schools in question were designated as previously
disadvantaged and the learners were from a poor socio-economic background. Both
schools were categorized as underperforming schools in the Orange Farm in 2011
based on the 2010 Grade 12 matric results. The number of learners targeted was 120
(40 learners per lesson) with mix genders. All learners agreed to participate in the study
and their parents also gave consent for them to participate in the study. All three
teachers agreed to participate in the study and principals of the school granted
permission to use their school for the research.
3.7 ANALYSIS OF DATA The objective of the first phase of the research was to investigate the performance of
grade 12 learners of 2008 in their national NSC chemistry examination and hence to
study their conceptual understanding of the levels of chemical representations. This
phase involved three stages, namely the preparation of the Classification Framework of
Chemical Representation (CFCR) for capturing the data, the collection of the data, and
analysis of the data using the computer software. The questions in a grade 12 national
chemistry examination were firstly analyzed and classified according to the chemical
representation demanded by each question. The questions were then placed into the 7
levels of categorization for chemical representation. The levels of categorization were:
macroscopic level, sub-microscopic level, symbolic level, macroscopic ↔ sub-
microscopic level, macroscopic ↔ symbolic level, sub-microscopic ↔ symbolic level,
and macroscopic ↔ sub-microscopic ↔ symbolic level. The quantitative data in the
form of the learner scores to each of the questions were analyzed statistically using the
PASW version 18.0 for windows software (SPSS). Using this software, the average
55
performance of learners at each of the levels of chemical representation was
determined. This quantitative data and their subsequent analysis provide a general
understanding of the research problem (Ivankova, Creswell, & Stick, 2006) and answer
the research question one. After the analysis, the results were studied and then
interpreted in Chapter 4 in addressing the first research question.
Figure 3.1: 1 st phase of data collection
Source: Prepared by the researcher.
The objective of the second phase of the research was to describe how teachers
facilitate learner conceptual understanding at the macroscopic, sub-microscopic and
symbolic levels of chemical representation. In this phase of the study, pre- interviews as
well as class observations were carried out to collect data required for the qualitative
research inquiry. These interviews and class observations were audio-taped, video-
taped and then transcribed.
According to Kvale (1996:189-190) the transcribed interviews should be interpreted by
the interviewer, either alone or with other researchers, the material is first structured,
then follows clarification by, for example eliminating digressions and repetitions and
distinguishes between the essential and the non-essential, the proper analysis involves
developing the meanings of the interviews, bringing the subjects’ own understanding
into the light as well as providing new perspectives from the researcher on the
phenomena. Data was analysed by using simple content analysis (Strauss & Corbin,
1990 and 1998). Then data was coded into small units of meaning. Open coding and
axial coding were used in the study to analyse the data. In open coding data is broken
down into concepts and categories and thereafter it is compared and grouped together
based on similarities and is given a conceptual label (Henning et al., 2004). In axial
coding parts of the data identified and separated in open coding is put back together in
Preparation of model Data Analysis of data
56
new ways to make connections between the categories (Henning et al., 2004). These
coded units of meaning were then categorized and analysed. This phase of the
research provided the answer to the second research question. The analysed data was
studied and interpreted in chapter 5. The result obtained in the qualitative research
inquiry assisted me in explaining and further interpreting the results obtained in
quantitative research inquiry in the first phase. The relationship between the two phases
in the study is represented below in figure 3.2.
Figure 3.2 : Representation of the research method
Source: Prepared by the researcher.
The first phase of the research gave a clear understanding of the performance of the
learners in responding to questions at the various levels of chemical representation in
the NSC chemistry examination of 2008. The second phase of the research revealed
the strategies used by the teachers to facilitate and convey the knowledge and concepts
at the three levels of chemical representations. This knowledge obtained from the two
phases of the research were then used in making recommendations that will enhance
Quantitative Research Method
Final Result (1)
Qualitative Research Method
Final Result (2)
Linking of Results of (1) and (2)
Outcome of the Research
Linking the Results
Phase 2
Phase 1
57
the facilitation as well as the performance of learners in responding to questions at the
three levels of chemical representation in future.
3.8 RELIABILITY AND VALIDITY Reliability can be defined as the accuracy or precision of an instrument that is used in a
research (Hudson, 1981). It refers to the consistency of a measure. An instrument is
reliable if the independent administrations of it or a comparable instrument consistently
yield similar results (de Vos & Fouche, 1998). Several methods can be used to establish
the reliability of an instrument such as the test-retest, and alternate form methods and
the split-half technique (de Vos & Fouche, 1998). Various tests such as the ANOVA and
the Kruskall-Wallis test were carried out in the first phase to establish the reliability of
the data collected. Reliability in relation to interviewing as a research method refers to
the degree of consistency that the interview has for the person or persons interviewed.
Reliability could be shown in two ways, either by repeating the interview on a later
occasion to find whether the same responses would be obtained or by examining the
extent to which the same questions given in a different form within the same interview
would elicit the same responses. Another aspect of reliability that is of vital significance
in research interviewing is the reliability of the interviewer (Keats, 2000). In this study
the researcher had conducted all the interviews and class observations. To improve the
reliability, multiple methods of data collection such as audio-taping, video-recording and
field notes were used to gather the data required for the study at the second phase.
Validity is concerned with how well the research instrument measures what it is
intended to measure. According to de Vos & Fouche, (1998), validity refers to the
degree to which an instrument is doing what is intended to do and an instrument may
have several purposes which vary in number, kind and scope. In interviewing research
validity relates to the level of confidence the researcher has that the content of the
interview is actually doing its intended job (Keats, 2000). The questions that were
formulated and asked at the pre- interviews were directly linked to the topic that was
researched. These questions have adequately covered the field that were researched in
58
terms of the chemistry content knowledge and the strategies used for the facilitation of
the conceptual understanding of chemical representation by learners.
3.9 CONCLUSION In this chapter, the research method and design were discussed. The two main phases
of the research process were outlined. In this study, I have utilised both quantitative and
qualitative research methodologies for the collection and analysis of data. In the first
phase of the study, five hundred chemistry exam scripts from the NSC examination from
the Gauteng Province were collected and analysed to establish the learner performance
in responding to questions at the macroscopic, microscopic and symbolic levels of
chemical representations.
A qualitative research methodology was utilised to collect and analyse data at the
second phase of the study. Pre-interviews and class observations were conducted to
gather data for this phase of study. Interviews and class observations were audio-taped,
video-taped and field notes were taken. These interviews and class observations were
then transcribed and analysed. Questions for the interviews were drawn to cover all the
aspects that were associated with the study in order to obtain a valid and reliable
response from the respondents.
In chapter four the quantitative data collected in the first phase were analysed,
interpreted and results discussed. Chapter five consists of the analysis and
interpretation of the qualitative data collected in the second phase of the study. The
result of the qualitative analysis of the data is also presented in this chapter.
59
CHAPTER FOUR
4. QUANTITATIVE ANALYSIS OF THE EXAMINATION SCRIPT DATA
4.1 INTRODUCTION In this chapter data was collected and analysed with regard to the first research
question on the performance of grade 12 learners in responding to questions at the
macroscopic, sub-microscopic and symbolic levels of chemical representation in the
2008 national examination.
A classification frame work of chemical representation (CFCR) was used to analyse the
data collected. The CFCR framework consists of seven categories namely macroscopic
level, sub-microscopic level, symbolic level, macroscopic ↔ sub-microscopic level,
macroscopic ↔ symbolic level, sub-microscopic ↔ symbolic level, and macroscopic ↔
sub-microscopic ↔ symbolic level. All the questions in the 2008 NSC Chemistry
question paper were classified under one of the levels using the above framework. This
grouping of questions was compared to the classification made by another experienced
researcher who also works in the science education field.
A content analysis was done with the grade 12, NSC chemistry learner scripts of 2008.
A complete analysis of learner scripts was done; marks were entered per question, and
then classified according to the CFCR framework. This data was then analysed
statistically using the PASW version 18.0 for windows software (SPSS) and the ANOVA
test was done for the different groups.
60
4.2 CLASSIFICATION OF QUESTIONS ACCORDING TO THE LEVELS OF CHEMICAL REPRESENTATIONS
A detailed description of the levels of classification of chemical representation was given
in chapter 2. The questions of the NSC 2008 chemistry question paper were classified
using the above framework.
4.2.1 Format of NSC, Chemistry question paper
The National Senior Certificate, chemistry question paper of 2008, contained two
sections, Section A and Section B. Section A comprises of four questions. In questions
1.1 to 1.5, learners were required to provide the scientific term relating to the description
provided. Questions 2.1 to 2.5 involved matching two columns. Questions 3.1 to 3.5
consisted of true/false items and question 4.1 to 4.5 were multiple choice questions.
Section B comprised of seven long questions and these tested problem solving ability,
the conceptual understanding of the three levels of chemical representations, the
understanding of scientific concepts and the relationship of chemistry with real-life
situations. The question paper covered the prescribed NSC (FET grade 10-12)
curriculum.
4.2.2 Classification of questions according to levels of chemical representation
The questions in the chemistry examination question paper were placed into seven
categories of chemical representation. These categories are: macroscopic level, sub-
microscopic level, symbolic level, macroscopic ↔ symbolic level, macroscopic ↔sub-
microscopic level, sub-microscopic level ↔ symbolic level, and macroscopic ↔ sub -
microscopic ↔ symbolic level.
The NSC Chemistry question paper of 2008 contained seventy two questions and these
questions were classified into seven levels, based on the conceptual understanding
required to answer those questions. Table 4.1 below shows how the questions were
classified.
61
4.2.3 The weighting of the classification There were 22 questions at the macroscopic level and these constituted almost 30.6%
of all questions. The sub-microscopic level constituted of eight questions and this made
up 11.1% of all questions. The symbolic level constituted of 16 questions and this
represented 22.2 % of the questions. The macroscopic to sub- microscopic level had
nine questions that had a percentage of 12.5%, macroscopic to symbolic category had
Table 4.1 Classification frame work of chemical
representations
Macroscopic level
Sub-microscopic level
Symbolic level
macroscopic ↔ sub- Microscopic level
macroscopic ↔ symbolic
sub – microscopic ↔symbolic
macroscopic
↔ sub-
microscopic
↔symbolic
Question question question question Question Question
Question
1.1 1.3 1.5 2.4 2.1 5.6 9.6.1
1.2 4.2 2.2 3.4 3.2 9.5 9.6.2
1.4 5.4 2.5 3.5 3.3 10.1.1 10.2.1
2.3 5.7.2 3.1 4.4 9.2 10.1.2
4.3 8.1.1 4.1 5.2 10.1.3 10.2.4
4.5 8.1.2 5.1 9.3 11.4 11.3
5.7.1 11.2 5.3 9.4 12.3.3
6.1.1 12.3.1 5.5 10.2.3 12.3.4
6.1.2 6.3 11.5
6.1.3 7.1 11.5
6.1.4 7.2
6.2 7.3
7.5 7.4
9.1 8.2.1
10.2.2 8.2.2
10.2.5 12.3.2 10.2.6 11.1 11.6 12.1 12.2 12.4
62
six questions and had 8.3 % and sub - microscopic to symbolic category had eight
questions with 11.1% of all questions. The macroscopic to sub- microscopic to symbolic
category had only 3 questions forming 4.2% of all questions in the paper. The
weighting and percentages of questions are shown in the table 4.2 below.
Table 4.2: The weighting and percentage distribution
Levels Number of
questions Total possible score
Weighting percentage (%)
Macroscopic level
22 24000 30.6
Sub-microscopic level
8 7500 11.1
Symbolic level
16 15000 22.2
Macroscopic to Sub- microscopic level
9 8500 12.5
Macroscopic to Symbolic
6 6500 8.3
Sub - microscopic to Symbolic
8 11000 11.1
Macroscopic to Sub- microscopic to Symbolic
3 2500 4.2
Total
72
75000
100.0
4.3 STATISTICAL ANALYSIS OF THE DATA
4.3.1 Descriptive for Percentage Acquired
The following table provides a descriptive statistics for the percentage acquired for all
72 questions. An overall average of 28.96% was acquired by the 500 learners with a
standard deviation of 18.23%. The lowest percentage obtained for a question was 0.4%
(Question 5.7.1) and the highest percentage obtained for a question was 70.5%
(Question 3.2). Half of the questions yielded acquired percentages of 24.7% or less.
63
Table 4.3: Descriptive for Percentage Acquired
Statistic
Mean 28.9553 Std. Deviation 18.23172 95% Confidence Interval for Mean Lower Bound 24.671 Upper Bound 33.2395 Median 24.7 Minimum 0.4 Maximum 70.5 Range 70.1
4.3.2 Distribution of percentages acquired
The distribution of percentages acquired for all 72 questions is shown in the following
histogram which is clearly skewed to the right, showing that the majority of questions
yielded percentages of less than 40%.
64
Figure 4.1 : Distribution of percentages acquired
4.3.3 Summary of the descriptive statistics for all seven categories
Of more interest, perhaps, is a breakdown of questions according to type. Similar
graphs now show how the questions in each type fared, starting with those in the
macroscopic level. Table 4.4 shows the average percentage marks obtained by learners
for each level of chemical representations and the table also shows the highest and the
lowest mark obtained by learners for questions at each level.
65
Table 4.4: Descriptive for Percentage acquired per question in each of the seven levels
N Mean (%)
Std. Deviation
(%)
Std. Error
95% Confidence Interval for Mean
Minimum Maximum Lower Bound
Upper Bound
Macroscopic level
22 30.9879 20.64035 4.40054 21.8365 40.1393 0.4 68.4
Sub-microscopic level
8 25.2625 18.01721 6.37005 10.1997 40.3253 6 52.6
Symbolic level
16 27.2458 15.22382 3.80596 19.1336 35.358 9.3 62.2
Macroscopic to Sub- microscopic level
9 36.3815 17.23271 5.74424 23.1353 49.6277 15.87 63.3
Macroscopic to Symbolic 6 41.7367 21.10333 8.6154 19.5901 63.8833 13 70.5
Sub - microscopic to Symbolic
8 17.3448 11.15862 3.94517 8.0159 26.6736 3.73 38.5
Macroscopic to Sub- microscopic to Symbolic
3 16.1333 8.23974 4.75722 -4.3353 36.602 8.4 24.8
Total
72 28.9553 18.23172 2.14863 24.671 33.2395 0.4 70.5
66
The following is a brief interpretation of the data presented in table 4.4
Macroscopic level:
Mean score: 30.9879%
There were twenty two questions under this category. The marks obtained by learners
for each question were converted into percentages for comparison purpose. The
average marks obtained by learners for each question under this classification is
30.9879% of the total marks allocated for the questions considered. The learners
obtained only 0.4% of the allocated marks for question 5.7.1 which is the minimum
score and the maximum percentage obtained in this category is 68.45% for question
2.3.
Sub-microscopic level:
Mean score: 25.2675%
Eight questions in the examination paper were identified as those related to the sub-
microscopic level. Learners obtained an average score of 25.2625% for this category.
The minimum score obtained by learners in this category is 6% for question 12.3.1. and
the maximum score they obtained is 52.6% for question 1.3.
Symbolic level:
Mean score: 27.2458%
There were 16 questions under this category and the average score obtained by
learners was 27.2458%. For question 7.4, the learners obtained the minimum marks of
9.3% and for question number 3.1 the learners obtained a maximum of 62.2%.
Macroscopic to sub- microscopic level:
Mean score: 36. 3815%
67
Nine questions were identified as the macroscopic to sub-microscopic level. The
average mark obtained for the category was 36.3815%. For question 9.4 learners
obtained only 5.87% which is the minimum score for the category and they obtained a
maximum mark of 63.3% for question 3.4.
Macroscopic to symbolic:
Mean score: 41. 7367%
There were six questions under this category. The average marks obtained by learners
for this classification is 41.736% which was the highest mean score obtained by
learners for all the categories. In this classification the minimum mark of 13% was
scored for question 11.4 and they obtained a maximum score of 70.5% for question 3.2.
The average mean score indicates that the learner responded better to questions that
were classified as macroscopic to symbolic level.
Sub-microscopic to symbolic level:
Mean score: 17.3448%
There were eight questions in this category. Learners obtained an average of 17.3448%
marks for the questions in this category. The minimum mark was obtained for question
12.3.4 which is just a mere 3.73% and they obtained 38.5% for question 11.3, which is
the maximum score for any question at this level.
Macroscopic to sub-microscopic to symbolic level:
Mean score: 16.1333 %
There were only three questions under this category. The average mark obtained for
this category is only 16.1333 %. This was the least average score they obtained for any
level of chemical representation. The minimum score obtained was 8.4 % for question
9.6.2 and the highest mark obtained was 24.8 % for question 9.6.1. Learner response to
questions in this category was the weakest among all the levels of chemical
68
representations. The average score obtained (28.9553%) indicates that the learner
conceptual understanding at this level is the weakest compared to other categories.
They presented the worst performance for this category of questions.
The Histogram for all categories of the CFCR is shown below. A summary of the
descriptive statistics for all question types will be given after all the seven histograms. In
the meantime, the mean, standard deviation and number of questions of each type is
presented next to each histogram so that one can compare the percentages acquired at
each level.
Figure 4.2: Descriptive statistics for macroscopic level
69
Figure 4.3: Descriptive statistics for sub-microscopic level
Figure 4.4: Descriptive statistics for symbolic level
70
Figure 4.5: Descriptive statistics for macroscopic to sub-microscopic level
Figure 4.6: Descriptive statistics for macroscopic to symbolic level
71
Figure 4.7: Descriptive statistics for sub-microscopic to symbolic level
Figure 4.8: Descriptive statistics for macroscopic to sub-microscopic to symbolic level
72
4.3.4 Comparative box-and-whisker plot From the values of the standard deviations in Table 4.4 above and the comparative box-
and-whisker plot below (Figure 4.9), it is apparent that percentages for the questions at
the macroscopic (20.64%) and the macroscopic to symbolic levels (21.1%) are rather
more variable than for those at the macroscopic to sub-microscopic to symbolic level
(8.24%). We can say that, for the latter group, the marks obtained were consistently
low, whereas some questions at the macroscopic level yielded high percentages and
others, very low. The percentages for the questions in the macroscopic to sub-
microscopic group did not dip quite as low as the other groups. More success, on an
average, was achieved in the questions at the macroscopic to symbolic level (M =
41.74%, SD = 21. 1%). It is also of interest to compare the minimum and maximum
percentages obtained for the questions at each level.
73
Figure 4.9: Comparative box-and-whisker plot
4.3.5 Analysis of variance There were clearly observable differences between the seven groups of questions.
Therefore, it was necessary to test whether these differences might be generalized to all
such questions, i.e. to test whether these differences were statistically significant or not.
A one-way analysis of variance is able to test whether the groups could be considered
the same on average, or not.
It was taken into account that in some groups there were only a few questions and that
there were no uniform group sizes. In order to do an Analysis of Variance, which is a
parametric test requiring rather strict assumptions to be met; the test for normality for all
seven groups as well as for equality of variances (or spread) was done.
74
Since all group sizes were below 50, the appropriate test for normality would be the
Shapiro-Wilk test, the results of which are shown in Table 4.5. The exceedence
probabilities (Sig.) are all greater than 0.05, evidence that the groups can all be
considered to have come from normal distributions.
Table 4.5: Tests of Normality
Group Shapiro-Wilk
Statistic df Sig. Percentage
acquired per
question
Macroscopic level
.940 22 .201
Sub-microscopic
level
.896 8 .267
Symbolic level
.927 16 .215
Macroscopic to Sub-
microscopic level
.922 9 .405
Macroscopic to Symbolic
.973 6 .912
Sub - microscopic to Symbolic
.936 8 .571
Macroscopic to Sub-
microscopic to Symbolic
.990 3 .812
75
To test the second assumption required, Levene’s test for Homogeneity of Variances
was done and a p-value of 0.307 was obtained (Table 4.6). Therefore, it was safely
assumed that this assumption too, has been met.
Table 4.6: Test of Homogeneity of Variances
Percentage acquired per question
Levene Statistic df1 df2 Sig.
1.222 6 65 0.307
Hence, it was possible to rely on the results of the ANOVA, Table 4.7 below. It appears
that the percentages acquired for the question types do not differ significantly on
average (F(6.65) = 1.758; p = 0.122). Small group sizes, however, cause the power of
a test to decrease so that there is not enough statistical evidence to demonstrate
significant differences among the group means seen in Table 4.6 above.
Table 4.7: ANOVA
Percentage acquired per question
Sum of Squares df
Mean Square F Sig.
Between Groups
3294.894 6 549.149 1.758 .122
Within Groups
20305.185 65 312.387
Total 23600.079 71 The Kruskall-Wallis test is non-parametric test that also compares more than two
groups like ANOVA does. It performs well for small groups that come from distributions
that violate the necessary assumptions for parametric tests. The results confirmed
those of ANOVA (p = 0.134). See Table 4.8.
76
Table 4.8: Test Statistics a,b
a. Kruskal Wallis Test
Percentage acquired per
question
Chi-square 9.795
df 6 Asymp. Sig. 0.134
Even though the differences between the means of any given pair of groups cannot be
shown to differ significantly, it is nevertheless of interest to consider them more closely.
The confidence intervals for the mean differences show how large or how small the
differences could have been and also that it could have been the mean of one group
being larger than another’s one time, and another time, the reverse situation - showing
once again the inconclusiveness of the results. (The Hochberg test is the appropriate
one to do post-hoc when the group sizes vary the way they do here. See table 4.4)
4.4 ANALYSIS OF LEARNER PERFORMANCE AND RESPONSES TO
QUESTIONS AT LEVELS OF REPRESENTATION The purpose of this research was to investigate the conceptual understanding of
learners at the different levels of chemical representation. In order to study this, the
learner performance at each level should be analysed separately. The following section
will give a detailed study of the learner performance based on their responses from their
scripts, at each category of the CFCR model.
77
4.4.1 Macroscopic category of classification
The macroscopic level forms the first category in the CFCR model. There were 22
questions in this category. These questions were related to the visible and real part of
chemistry.
Table 4.9 gives an analysis of marks obtained for the macroscopic category. Among all
the questions, 5.7.1 was the worst answered question in this category and a sample of
500 learners obtained only four (4) marks out of a possible mark of 1000.The best
performed question was 2.3 with a percentage of 68,4, and the second best was
question 10.2.6 with a percentage of 64,0. In four questions (5.7.1, 7.5, 10.2.2, and
11.6) learners obtained below 10%; four questions (6.1.4, 9.1, 6.2, and 12.1) learners
obtained between 10% and 20%. In six questions (2.3, 4.3, 4.5, 6.1.1, 10.2.6 and 6.1.1)
learners obtained 50% and above.
Table 4.9: Macroscopic category of classification
Macroscopic category of classification
Que
stio
n
num
ber
Mar
k pe
r qu
estio
n
Tot
al
poss
ible
m
ark
for
the
sam
ple
Tot
al a
ctua
l m
ark
obta
ined
for
the
sam
ple
Per
cent
age
obta
ined
per
qu
estio
n by
sa
mpl
e
1.1 1 500 123 24.6
1.2 1 500 132 26,4
1.4 1 500 125 25 2.3 1 500 342 68,4 4.3 3 1500 846 56.4 4.5 3 1500 902 60 5.7.1 2 1000 4 0.4 6.1.1 2 1000 570 57 6.1.2 2 1000 509 50,9 6.1.3 2 1000 382 38,2 6.1.4 4 2000 385 19,25 6.2 2 1000 122 12,2 7.5 2 1000 41 4,1 9.1 4 2000 257 12,85 10.2.2 2 1000 94 9,4 10.2.5 2 1000 296 29,6
78
10.2.6 2 1000 640 64,0 11.1 2 1000 358 35,8 11.6 2 1000 78 7,8 12.1 4 2000 316 15,8 12.2 2 1000 318 31,8 12.4 2 1000 317 31,7
The following is a brief discussion of the difficulties experienced by learners in
answering some of the questions for which learners attained very low marks and are
classified at the macroscopic level. The macroscopic level of chemical representation is
the real and visible part of chemistry.
Question 6 was formulated as follows: “You have two test tubes containing equal
amounts of compounds X and Y respectively as given in figure. Both have the same
molecular formula C5H10.You have to distinguish which compound is saturated. You
hypothesise that compound X is saturated.”
X y
Question 6.1.4 was formulated as follows: “Write down the procedure you will follow”. The learners were required to explain the procedure that they would follow to identify
the saturated compound. The learner was supposed to explain the following:
• Add equal volumes of bromine water/ iodine solution to both compounds X and Y
in the test tubes.
C5H10
C5H10
79
• Compare /observe the colour change for the two compounds.
Most of the learners did not answer the question. One common difficulty noticed was
that learners were unable to understand what was required of them in answering the
question.
Question 6.2 required learners to: “Describe how you will use your observations to verify
your hypothesis”.
The learners had to observe the reaction in 6.1.4 to answer this question. The expected
learner answer could be the following:
• The solution that showed a rapid colour change was unsaturated; or
• The solution that shows no or a slow colour change (no reaction takes place) is
saturated.
The common difficulty identified was that learners were unable to understand what was
expected of them in answering the question. Learners were expected to verify whether
they made the correct hypothesis using the observation they had in question 6.1.4.
They failed to link the concept that the unsaturated hydrocarbons consist of a double or
a triple bond between the carbon atoms and are unstable. Therefore, the bromine
solution or iodine solution will discolour quickly in an unsaturated solution while no
discolouring or slow colour change will be observed in an unsaturated solution. In a
saturated solution the existing bonds have to be broken down and new bonds have to
be established and this requires energy and hence no reaction and colour change. The
learners failed to identify the solution in which quick discolouring of the bromine/ iodine
solution took place as unsaturated and the solution in which no discolouring occurred as
saturated solution and use this knowledge to verify their hypothesis.
4.4.2 Sub-microscopic category of classification and learner performance
This is the second category in the CFCR model of chemical representation. There were
eight questions in this category. There were three questions that carried one mark, two
80
questions that carried 2 marks, one question with three marks and one question with 4
marks. The lowest percentage obtained (12.3.1) was 6.0% and 500 learners obtained
only thirty marks of a possible 500. The second lowest percentage obtained was 6.8
(question 5.7.2) of a possible 500 marks. Five- hundred learners obtained only 34
marks instead of 500. Again, the percentage obtained for question 8.1.1 was 9.5% and
five hundred learners received 95 marks of a possible mark of 1000. The highest scored
question was 1.3 (52%) and five hundred learners obtained 263 of a possible 500
marks.
Table 4.10: The sub-microscopic category of classification
Que
stio
n nu
mbe
r
Mar
k pe
r qu
estio
n
Tot
al p
ossi
ble
mar
k fo
r th
e sa
mpl
e
Tot
al a
ctua
l mar
k ob
tain
ed fo
r th
e sa
mpl
e
Per
cent
age
obta
ined
per
qu
estio
n by
sa
mpl
e
1.3 1 500 263 52,6
4.2 3 1500 435 29,0
5.4 4 2000 584 29,2 5.7.2 1 500 34 6,8 8.1.1 2 1000 95 9,5 8.1.2 2 1000 210 21,0 11.2 1 500 240 48,0 12.3.1 1 500 30 6,0
The following is a brief discussion of the common difficulties experienced by learners in
answering some of the above questions for which they obtained very low marks.
Question 8.1.2 was formulated as follows: “In terms of the collision theory, explain why
the rate of a chemical reaction increases with increasing temperature”.
In order to answer this question, learners needed to know the sub-microscopic level of a
chemical reaction such as the effect of temperature on the reaction rate. According to
the collision theory, a chemical reaction can only occur between particles (ions, atoms
81
or molecules) when they collide. Increase in temperature means particles move faster
or have sufficient kinetic energy which results in more effective collisions hence the
increased reaction rate. Most of the learners explained that as the temperature
increased, the speed of reaction also increased but they did not answer in terms of the
collision theory of particles. Learners were expected to indicate that, an increase in
temperature of the system increases the average kinetic energy of the particles. Hence
they will move faster and increase the rate of collision. This implies that more products
are formed at a faster rate which means, the rate of the chemical reaction increases
with temperature.
4.4.3 Symbolic category of classification and learner performance This is the third category of the CFCR frame work of chemical representation. There are
sixteen questions in this category. In chemistry, both macroscopic as well as sub-
microscopic explanations are explained using the symbolic representations. Symbolic
representations can be formulae, equations, graphical representations, models,
analogues, etc.
Question 7.4 was poorly answered with a score of 9.3%. Five hundred learners scored
93 marks out of a possible mark of 1000. The next poorly answered questions were 6.3
and 12.3.2 and each of them scored 10.8% and 10.0% respectively. The highest scored
question was 3.1 in which learners scored 62.0%.
Table 4.11: The symbolic category of classification
Symbolic category of classification
Que
stio
n nu
mbe
r
Mar
k pe
r qu
estio
n
Tot
al p
ossi
ble
mar
k fo
r th
e sa
mpl
e
Tot
al a
ctua
l mar
k ob
tain
ed fo
r th
e sa
mpl
e
Per
cent
age
obta
ined
per
qu
estio
n by
sa
mpl
e
1.5 1 500 107 21.4
2.2 1 500 216 43,2
2.5 1 500 82 16,4
3.1 2 1000 622 62,0
4.1 3 1500 537 35,8
82
5.1 2 1000 476 47,6
5.3 1 500 184 36,8
5.5 3 1500 452 30,13
6.3 2 1000 108 10,8
7.1 1 500 110 22,0
7.2 2 1000 187 18,7
7.3 1 500 112 22,4
7.4 2 1000 93 9,3
8.2.1 4 2000 708 35,4
8.2.2 1 500 69 13,8
12.3.2 3 1500 150 10,0
The following is a brief discussion of the common difficulties experienced by learners in
answering some of the questions categorized as at symbolic level. These were the
difficultied noticed in the learner answers for questions for which they scored low marks
QUESTION 7: More than 90 million organic compounds are known to man today. In the
table below the letters A to E represent a few of these compounds.
COMPOUND A
CH3 CH2CH2 COH
║ O
B
Trimethylamine
C
CH3 − CH − CH3
║
OH
D 6-methyl-1-heptene
E
O CH3
CH3 C N CH3
Question 7.1 was formulated as follows: “Write down the IUPAC name of compound A”
83
By looking at the structure of the compound learners should be able to write the name
of the compound as butanoic acid.
The following were some of the common difficulties identified :
• Learners struggle to identify the compound as an organic acid
• Learners were unable to give the correct prefix in the name based on the number
of carbon atoms.
Question 7.2 was formulated as follows: “Write down the structural formula of the
compound D”.
This question is a symbolic level of representation. Learners needed to answer
the question by analysing the name of the compound as given below.
Very few learners got the answer correct for the above question. The following are
some of the common difficulties identified:
• Learners could not understand the meaning of the prefix attached to the name of
the hydrocarbon which indicated that there were seven carbon atoms in the
compound. They also failed to identify that the compound was an alkene since its
name ended with an – ene.
• Learners also failed to understand and interpret the meaning of the numbering
system that was used in naming the organic compound to specify the position of
the double bond and the alkyl group attached to it. They failed to understand that
the double bond should be placed after the first carbon atom and the methyl
group should be attached to the sixth carbon atom.
84
4.4.4 Macroscopic sub-microscopic category of classification and learner
performance
This is the fourth category of the CFCR model of chemical representation.
There were nine questions in this category. The poorly answered question in this
category was 9.4 with a percentage of 18.4. The best performed question was 3.4 with
a percentage of 63.3 and 500 learners obtained a total mark of 633 out of the possible
1000 marks.
Table 4.12: Macroscopic sub-microscopic category of classification
Macroscopic↔ sub-microscopic category of classification
Que
stio
n nu
mbe
r
Mar
k pe
r qu
estio
n
Tot
al p
ossi
ble
mar
k fo
r th
e sa
mpl
e
Tot
al a
ctua
l m
ark
obta
ined
fo
r th
e sa
mpl
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Per
cent
age
obta
ined
per
qu
estio
n by
sa
mpl
e
2.4 1 500 271 54,2 3.4 2 1000 633 63,3 3.5 2 1000 250 25,0 4.4 3 1500 556 37,07 5.2 2 1000 461 46,1 9.3 1 500 235 47,0 9.4 3 1500 238 15,87 10.2.3 1 500 92 18.4 11.5 2 1000 205 20,5
There were nine questions in this classification of questions. Some of the difficulties
experienced by the learners when they answered the question 11.5 for which they
obtained very low mark are given below.
Question 11 was about extraction of aluminium at a temperature as high as 1000°C.
Carbon electrodes are used in the extraction furnace.
85
Question 11.5 was formulated as follows: “Why should the carbon electrodes be
replaced regularly?
Learners needed to shift between the macroscopic level and sub-microscopic
level. The carbon electrode became thinner and thinner which was the macroscopic
level of the observation. The reason for this could be explained under the sub-
microscopic level as carbon was used up and was oxidised by losing electrons and
needed to be replenished. From the learners’ responses, it was evident that many of
them did not know that the carbon rod was used-up or oxidised and hence no plausible
explanation could be offered at the sub-microscopic level.
4.4.5 Macroscopic symbolic category of classification and learner
performance This category of classification contained six questions. In this category, the
transformation was from macroscopic to symbolic and vice versa. The poorly answered
question in this category was 11.4 with a mark of 13%. The best performed question in
this category was 3.2 for which they obtained 70.5% and 500 learners obtained a total
mark of 705 out of the possible 1000 marks.
Table 4.13: Macroscopic↔ symbolic category of classification
Macroscopic↔ symbolic category of classification
Que
stio
n nu
mbe
r
Mar
k pe
r qu
estio
n
Tot
al p
ossi
ble
mar
k fo
r th
e sa
mpl
e
Tot
al a
ctua
l mar
k ob
tain
ed fo
r th
e sa
mpl
e
Per
cent
age
obta
ined
per
qu
estio
n by
sa
mpl
e
2.1 1 500 287 57,4
3.2 2 1000 705 70,5
3.3 2 1000 436 43,6
9.2 1 500 211 42,2
10.1.3 5 2500 593 23,72
11.4 2 1000 130 13.0
86
Some of the common difficulties experienced by learners in answering question 11.4
are given below.
Question 11 was formulated as follows: “Aluminium is one of the most abundant metals
on earth, yet it is expensive-largely because of the amount of electricity needed to
extract it. Aluminium ore is called bauxite. The bauxite is purified to yield a white
powder, aluminium oxide, from which aluminium can be extracted. The diagram below
shows an electrolyte cell used for the extraction of aluminium at temperatures as high
as 10000C”.
Question 11.4 was formulated as follows: “Why should the carbon dioxide gas form at
one of the electrodes”.
Most of the learners were unable to understand what was expected of them in
answering the above question. Learners had difficulty in identifying the oxidation and
the reduction process that were involved in the raction. Therefore, they coluld not write
down the equations for the oxidation and reduction half- reactions and use them to
answer the above question. It was also noticed that 500 learners managed to obtain
only 130 marks out of a total of 1000 marks for this question. This was a clear indication
of the degree of difficulty they had experienced in understanding the question.
87
They could have mentioned that the electrolysis of cryolite solution gives aluminium at
the cathode and oxygen at the anode. The formation of aluminium and oxygen could be
explained using the following half reactions.
Al3+ + 3e- Al (aluminium metal at the cathode)
2O2- O2 + 4e- (oxygen at the anode)
In this question learners needed to shift from macroscopic level to symbolic level of
explanation. At the macroscopic level they could observe the production of CO2 gas
which was the result of burning carbon in oxygen at high temperature. This could
further be explained in the symbolic form as:
C (s) + O2 (g) → CO2(g) / C (s) + 2O2- (g) → CO2 + 4e-
4.4.6 Sub-microscopic symbolic category of classification and learner
Performance
This is the sixth category of the CFCR frame work of chemical representation.
There were eight questions in this category. The most poorly answered question in this
category was 5.6 for which they obtained only 7.1% of the marks allocated. The best
performed question was 11.3 for which they scored 38.5%. The total marks obtained by
500 learners for this question was 385 out of a total of 1000 marks.
Table 4.14: Sub-microscopic →symbolic category of classification
Sub-microscopic ↔ symbolic category of classification
Que
stio
n nu
mbe
r
Mar
k pe
r qu
estio
n
Tot
al p
ossi
ble
mar
k fo
r th
e sa
mpl
e
Tot
al a
ctua
l mar
k ob
tain
ed fo
r th
e sa
mpl
e
Per
cent
age
obta
ined
per
qu
estio
n by
sa
mpl
e
5.6 2 1000 71 7,1
9.5 8 4000 801 20,03
88
10.1.1 2 1000 227 22.7
10.1.2 1 500 77 15,4
10.2.4 2 1000 223 22,3
11.3 2 1000 385 38,5
12.3.3 2 1000 90 9,0
12.3.4 3 1500 56 3.73
Question 10.1.1 was referred to the following redox reaction:
Fe(s) + O2(g) + H2O(l) → Fe2+ (aq) + OH-(aq)
The question required the learners to write down the oxidation half-reaction. This
question required learners to engage at the sub-microscopic level in identifying the
substance that is being oxidised. Thereafter, they needed to shift to the symbolic level
to be able to write down the half reaction. However, from the learner response, it was
evident that most of the learners failed to understand the sub-microscopic part of the
above question.
Most of the learners knew that electrons played a part in the oxidation half-reaction. The
misconceptions varied from learner to learner. Some learners believed that the iron
atom received electrons to change into its ionic form. The inability of learners to
distinguish between oxidation and reduction process was observed in their answers to
the above question. Therefore, they experienced difficulty in transforming the concepts
at sub-microscopic level to symbolic level using the oxidation half-reaction. They were
expected to answer the above question using the following oxidation half- reaction.
Fe Fe2+ + 2e-
Question 11.3 was referred to the extraction of aluminium from its ore, the bauxite. The
learners were asked to write down the half-reaction for the formation of aluminium using
the Table of Standard Reduction Potentials.
89
Learners had once again exhibited their difficulty in understanding the concepts of
oxidation and reduction in terms of electron transfer. Many learners had failed to identify
the fact that aluminium ions had received three electrons each to change to its atom.
They could not locate the equation that represented the reduction half-reaction of
aluminium ion from the Table of Standard Reduction Potentials. Therefore, most of
them had difficulty in writing the equation that represented the reduction half-reaction for
the formation of aluminium. The possible answer could have been as follows.
Al3+ + 3e- → Al
It was also observed that learners could not distinguish the meaning between double
and single arrows as well as forward and reverse arrows.
Question 12.3 referred to the flow diagram below which represented the conversion of
ammonia into nitrates.
Process X
Question 12.3.3 was formulated as follows: “Write down the formula for gas Y”.
Learners were required to know the product of the reaction between NH3 and NO as
NO2. Again they needed to know the valences / oxidation numbers of both nitrogen and
oxygen. There should be a shift from the sub-microscopic level of knowledge to the
symbolic level of knowledge of representation.
It was evident from the learner scripts that many of the learners were not aware of the
product, NO2 which was a gas and hence failed to answer the question correctly.
Some of the answers they wrote were as follows: CO2: 2 H2O; NH3NO; N2OH3; ….
NH3 (g) NO Gas Y
Liquid Z
Fertiliser
90
Question 12.3.4 was formulated as: “Write down a balanced equation for the
preparation of fertiliser P”.
In order to answer this question, learners were required to know the compound, liquid Z
and the reaction between NH3 and the liquid Z as well as the product formed. First of all,
learners were supposed to engage with the sub-microscopic level to identify the
changes that occurred at the molecular level during the chemical reaction. Thereafter,
they needed to know the formula of liquid Z and fertiliser P to write the equation of the
reaction at the symbolic level. Liquid Z was nitric acid and its formula is HNO3.
Learners were expected to state that nitric acid eventually reacted with NH3 to form
ammonium nitrate (NH4NO3) as per the following equation.
NH3 (g) + HNO3(aq) → NH4NO3(s)
It was noted from the scripts analysis that:
• Many of the learners did not know the name or formula of liquid Z;
• Many of them lack the ability to comprehend the flow diagram and they could not
identify the reactants from the equation and most of them wrote irrelevant
answers.
4.4.7 Macroscopic Sub-microscopic symbolic category of
classification and learner performance
This is the seventh and the last category of the CFCR frame work of chemical
representation. There were only three questions in this category. There were some
questions that needed knowledge of all three levels to answer it. The poorly answered
question in this category was 9.6.2 for which learners scored 7.1%. The best performed
question in this group was 9.6.1 for which they obtained 24.8% and 500 learners
obtained a total mark of 124 out of a possible 500 marks.
91
Table 4.15
Macroscopic Sub-microscopic symbolic category of classification
Que
stio
n nu
mbe
r
Mar
k pe
r qu
estio
n
Tot
al p
ossi
ble
mar
k fo
r th
e sa
mpl
e
Tot
al a
ctua
l mar
k ob
tain
ed fo
r th
e sa
mpl
e
Per
cent
age
obta
ined
per
qu
estio
n by
sa
mpl
e
9.6.1 1 500 124 24,8
9.6.2 2 1000 84 8,4
10.2.1 2 1000 152 15,2
The following is a brief summary of the common difficulties experienced by learners
when they answered the question 10.2.1.
Question 10.2.1 was formulated as follows: “Magnesium is used to protect underground
pipes against rusting. The diagram below shows an iron pipe connected to a
magnesium bar. Use the Table of Standard Reduction Potentials to explain why
magnesium can be used to protect an iron pipe against rusting”.
Learners were expected to transform the concepts from one level to another while they
were answering the question. This question required learners to transfer concepts
among the three levels of chemical representations namely the macroscopic, sub-
92
microscopic and symbolic levels. Rusting is a common phenomenon that everyone is
familiar with. Learners needed to explain the concept of rusting at the sub-microscopic
level using the symbolic level of chemical representation. They could explain this
concept using the redox-reactions.
Learners could explain the process of rusting as follows: Mg is a stronger reducing
agent than iron and will be oxidised more easily than Fe. Since Fe is a weaker reducing
agent than Mg it will not be oxidised. This means that Fe will not lose its electrons easily
compared to magnesium and therefore, it will not be oxidised easily. This reaction could
be represented using the following half reaction.
Mg → Mg2+ + 2e-
It was observed from the script analysis that learners had difficulty to interpret the
arrangement of elements in the Standard Electrode Potential Table. Most of the
learners could not identify the stronger reducing agents from the table provided to them.
Therefore, they had difficulty in identifying magnesium as a stronger reducing agent
than iron or iron as a weaker reducing agent than magnesium.
4.5 CONCLUSION In this chapter, a quantitative research methodology was utilised to study the grade 12
learner’s conceptual understanding of chemical representation. Five hundred learner’s
answer scripts from the 2008 NSC examination from the Gauteng Province were
analysed and the data collected were analysed and studied. A classification framework
of chemical representation (CFCR) was used to analyse the data collected. After a
complete analysis of the learner scripts, the marks were entered per question, and then
classified according to the CFCR framework. This data was then analysed statistically
using PASW version 18.0 for windows software (SPSS) and the ANOVA test was done
for different groups.
93
A summary of the descriptive statistics for all seven categories of chemical
representation as well as histograms that represents the above for each level was also
presented in this chapter. An analysis of learner performance and responses to
questions at different levels of representation was also done in this chapter. Common
difficulties experienced by learners in answering specific questions at different levels for
which they obtained very low marks were also briefly explained in this chapter. The
average percentage mark obtained for the seven levels of chemical representation was
28.9553%. This implies that most of the learners lack a deeper conceptual
understanding of the levels of chemical representation. In chapter 5 the strategies used
by the teachers to facilitate the concepts and knowledge will be analysed. These
findings will be used to make recommendations to improve the performance of learners
in responding to questions at different levels of chemical representation.
94
CHAPTER FIVE
5. QUALITATIVE DATA ANALYSIS
5.1 INTRODUCTION The first aim of this research study was to investigate the conceptual
understanding of chemical representations at macroscopic, microscopic and
symbolic levels by grade 12 learners in the NSC examination. In this chapter,
I address the second aim of the study, namely to identify the strategies used
by teachers in facilitating learner conceptual understanding at the
macroscopic, microscopic and symbolic levels of chemical representation. A
qualitative research methodology was utilised for the collection of data as well
as the analysis of this data. Pre- interviews as well as class observations were
carried out to collect the required data.
5.2 PARTICIPANTS IN THE STUDY The three participants in the study were grade 10-12 physical sciences
teachers with similar backgrounds from two schools from the same township.
Convenient sampling was used to select the participants for the study.
Learners who were selected to participate in the study were all in grade 11
physical sciences class from the two schools where the participant teachers
are currently employed. Three classes of 40 learners each were selected to
participate in this research study. The group consisted of both male and
female learners.
5.2.1 Teacher profile During the first meeting with the three educators, I managed to collect the
details of their teaching experience and qualifications from which a profile was
prepared for them. In order to protect the identities of all participating
teachers’ and schools, pseudonyms have been used. The teachers profiles
are given below:
95
Table 5.1:Profile of teachers
Name of teachers Qualification Teaching
experience Position held at school
Mrs. Mbele
STD ( chemistry & life sciences);
FDE(Education Management);
BEd (Education Management)
13 Deputy principal
Mr. Mashigo
STD (physics & mathematics) 15 HOD
Mrs. Khumalo
BSc (Hons) chemistry
BEd (Hons) Education Management
and Leadership
12 years HOD
5.2.2 School profile In order to keep the identity of the schools anonymous, the schools are
referred to as school X and school Y. School X is situated in a previously
disadvantaged township. Most learners reside in the township itself, while
other learners live in neighbouring informal settlements. Most parents are
unemployed and illiterate. Many learners are coming from child-driven families
where there is no one to guide or support them. The Gauteng Department of
Education (GDE) has a feeding scheme programme for disadvantaged
learners in the province and this school is part of this programme. All learners
are fed once a day. School X has a very good infra structure with an
administration block and specialist rooms. It has one fully equipped science
laboratory and all learners have textbooks. Mrs Mbele and Mr Mashigo are
currently employed at this school and they teach physical sciences at the FET
(grade 10-12) phase.
Mrs Khumalo is currently employed at school Y and it is also situated in a
previously disadvantaged township. About forty percent of the learners who
attend this school come from the nearby informal settlements. Most parents
96
are unemployed and illiterate. As is the case with school X many learners,
come from child-driven families where there is no one to guide or support
them. All learners are fed everyday at school from the GDE funding. This
school also has a very good infrastructure including a science laboratory.
However, the laboratories were not sufficiently equipped to perform necessary
experiments that are relevant to the chemistry curriculum.
5.3 PRE-INTERVIEW A pre-interview was conducted with each of the three teachers before the
lesson observations. The purpose of the interviews was to elicit data on how
teachers plan their lessons in engaging learners at the levels of chemical
representation. Semi-structured and descriptive pre-interviews were
conducted by the researcher with all three participants (Appendix, E). The
interview with each educator lasted for 20-25 minutes. The interviews were
audio-taped, transcribed verbatim and analysed.
5.3.1 Themes and sub-themes of pre-interview
The interview transcripts were coded. These interviews and field notes were
coded. Open coding and axial coding were used in this study to analyse the
data and to formulate sub-themes and themes. After coding the transcripts
they were analysed and categorised into subthemes. From these subthemes
three themes emerged. These themes and sub-themes are presented in
Table 5.2 below:
97
Table 5.2: Themes and sub-themes of pre-interview
Codes Sub-themes Themes
symbols, formulae ions, equations structural formulae diagrams, chart macroscopic microscopic symbolic
learning difficulties writing symbols and formulae writing chemical equations calculations
Teachers maintain that learners find chemistry concepts to be abstract
demonstration group work lecture method precipitation covalent bonding acid –base reaction precipitation reactions,
practical orientated teaching no conception of levels of representation
Teachers use a variety of strategies in facilitating conceptual understanding in chemistry
equipped laboratory apparatus chemicals teaching aids
laboratory science equipments chemicals
Teachers bemoaned the lack of physical resources in experiments in chemistry
Source: Prepared by the researcher
5.3.2 Analysis of Data Collected During Pre- Interview The purpose of the second research question was to identify the strategies
teachers use to facilitate the conceptual understanding at the macroscopic,
sub-microscopic and symbolic levels of chemical representation. Although
four themes had emerged from the data, some themes overlapped as evident
from the following discussions. The themes and sub-themes are explained
below.
98
5.3.2.1 Teachers maintain that learners find chemistry concepts to be abstract Chemistry is an abstract subject and it has become a difficult subject for
learners to learn. All three teachers maintained that learners encountered
difficulty in chemistry, as they found chemistry concepts to be abstract. The
teachers believe that learners have a particular difficulty with chemical
symbols, formulae and writing equation. Mrs Mbele explained that she used
the Periodic Table to teach symbols of elements. She explained:
“Learners have difficulties in learning symbols and chemical formulae.
The manner in which I teach them, I normally have a periodic table
whereby it will have the symbol and the name under it, because you’ll
find some of the symbol, …, you find some of the elements in the
periodic table they are not the same as the, like take for an example
lead. Lead, the symbol is Pb but the manner in which you write it is
lead. So I normally tell them that it’s not always going to be the first
letter of the symbol like in oxygen”.
Because learners had problems in writing symbols and formulae they were
not in a position to write chemical equations. Mrs Khumalo states:
“I think, my learners are encountering lots of difficulties in learning
chemistry. For example, when you ask them to write the equation, it is
difficult for them…So to know the whole concept of Chemistry, without
knowing the formulas, it’s difficult”.
It is clear that teachers need to more explicitly address the learning of
symbols, and equations in their classrooms.
In order for learners to write a formula, teachers need to spend more time in
helping learners grasp the concept of valency. In this way learners will come
to understand how molecules have a particular formula.
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5.3.2.2 Teachers use a variety of strategies in facilitating conceptual
understanding in chemistry
Common strategies used by teachers included demonstrations, having
learners do practical work and explanations.
In order to get an insight into the strategies employed, I asked all three
teachers how they would teach covalent bonding. Mr Mashigo explained that
he would use the periodic table to firstly teach learners about valency so that
the learners could understand elements formed a single, double or triple
bond. He explained this as follows:
“I start first by introducing them to the periodic table, elements certain
particular group can form one bond, another one can form a double
bond and so on.”
Mrs Khumalo adopted another strategy in that she would firstly introduce
learners to a variety of chemical reactions, and then explain covalent bonding
as a case of bonding between elements in a gas. This was evident from the
following excerpt:
“I will teach covalent bonding by using a chemical reaction, bonds are
broken, ions are formed, then the positive and negative ions will attract
each other to form the compound”.
The approach adopted by Mrs Mbele was unclear as she mentioned that:
“I start by explaining to the learners what type of bond you get in gases.
If you have carbon and oxygen what type of bond is found there …. And
explain how covalent bond is formed starting from what type of bond is
found between this and this”.
I also questioned teachers on the approach they take when teaching about
the formation of precipitates. Mr Mashigo explained the formation of
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precipitates in terms of the reactivity of elements. He gave the example that “if
chlorine is added to a solution of potassium bromide then because chlorine is
more reactive than bromine, then bromine will settle at the bottom”. Mrs
Khumalo demonstrated to her learners the formation of precipitates in solution
by mixing together a combination of different salt solutions. Mrs Mbele replied
that precipitation reaction was a challenging topic for her and she always
asked her colleague to teach the learners.
All three teachers had different views on how to teach acid- base reactions
and writing of equations. Mrs Khumalo appeared to adopt an approach
whereby she firstly explained the formation of the ions in solution by the acid
and the base, and then how the ions combine to form the products. She
explained this as follows:
“I first teach there is a term dissociation, whereby when an acid meets
with something, it dissociates into ions. The same with bases also and
the positive will be attracted to a negative in a base and vice versa so
that you can get the product, the salt and water….I like to do practical
in acid and base”.
Mr Mashigo used a similar approach and explained how he taught the
reaction between hydrochloric acid and sodium carbonate:
“You’ll have hydrogen and a chloride ion and then from a carbonate,
say for instance.. sodium carbonate, then you’ll have that sodium and
then I tell them from one substance one with a positive ion will combine
with the one with a negative ion from the other substance. Then I show
them how they combine and then I explain that now from, that CO32-
,
one oxygen will come out and combine with that hydrogen from water.
And then what is left now? Then I ask them: if I take away one oxygen
atom, what is left? And they will know that now it will be carbon dioxide
and then they understand that now, how the acid and the base
reacted”.
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All three teachers took every opportunity at engaging learners at the
macroscopic level when teaching chemistry. They believed that it makes the
learning of concepts to become more concrete. In this regard the teachers
remarked that learners enjoyed doing structured practical activities where they
are given a worksheet with instructions to be followed. Mr Mashigo remarked
that:
“learners have no problem in performing experiments, chemistry
experiments…..I always guide them by giving worksheets that shows,
how to go about and then they themselves can be in a position to
identify variables and all that. Although somewhere I need to guide
them towards some variables”.
According to Mrs Khumalo:
“They don’t have difficulty as long as they have instructions. …To write
down the investigative question and hypothesis, they are having
problems…but once they have everything, they can do that practical”.
It is evident from the interview that teachers adopt a variety of strategies in
engaging learners at the macroscopic, symbolic and sub-microscopic levels of
chemical representation. At the macroscopic level teachers either do a
practical demonstration, or depending on the availability of resources they
have learners do a practical activity. At the symbolic level, teachers refer the
learners to the periodic table as a point of reference in teaching the chemical
symbols of elements. The learners are expected to remember the symbols.
They teach the writing of chemical formulae by explaining to learners the
concepts of valency and bonding between elements. Following on this
teachers teach the writing of chemical equations by showing learners on the
board how bonds in the reacting substances are broken and new bonds are
formed leading to products. In teaching the writing of chemical equations
teachers also invoke the macroscopic level of representation as they
demonstrate a chemical reaction that corresponds to the chemical equation.
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5.3.2.3 Teachers bemoaned the lack of physical resources in experiments in chemistry
Although teachers recognise the importance of engaging the learners at the
macroscopic levels in trying to make the learning of chemistry concepts more
concrete and accessible to learners, a significant constraint in achieving this
through practical work was the lack of resources. All the teachers had
complained about the condition of the laboratories at their schools. They
informed that those laboratories are physical structures without proper tables,
cupboards or running water.
Mrs Mbele explained this as follows:
“The challenges are the equipment because the schools are, poorly
resourced. Sometimes if you want to do an experiment you have to go
in to your pocket to do that. Hai, I can say always because if take for
an example you want to use a gas burner, we don’t have gas, you have
to buy spirit for the burner from your pocket. Because we are struggling
to get help”.
Mrs Khumalo is also of the opinion that there was not much help from the
principal or school governing body to buy resources when it was needed. Mrs
Khumalo expressed this as follows:
“If I don’t have enough chemicals…. let’s say in the boxes. It’s better, if
some of the things I can buy them. For example, there was, practical
on rates of chemical reactions. I have to take out money and buy the
Cal-C-Vita to do the practical so that learners can see. But if there are
no chemicals it’s difficult. But at times we need something, they take
their time. Because it must start from the principal, by SGB before they
can buy anything”.
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It is clearly evident that despite the imperative for practical work to be done,
teachers are frustrated in their efforts to infuse more practical work into their
teaching by the lack of chemical and apparatus.
5.4 LESSON OBSERVATION
I observed a chemistry lesson taught by each of the three teachers. I was a
non-participant observer. All lessons were audio-taped and later transcribed
for further clarification and validity. During the lesson, the teachers’ teaching
methods and techniques, resources used during interaction with the class,
learner response to questions, and the learner activities were noted. The
three lessons are now described, with particular reference to teacher
facilitation of concepts at the three levels of chemical representation.
5.4.1 Lesson observation: Mrs Khumalo She had a class of 40 learners from grade 11 for the lesson in the laboratory
of the school. The duration of the period was one hour and the topic for the
lesson was acid- base reactions
Lesson plan for the lesson was available and handouts for the learners were
also prepared in advance. The teacher asked questions to test the prior
knowledge of the learners. The teacher did not give any class work,
assessment but a home work was given. The teacher did not review the
concepts she taught during the lesson. Learners were passive and most of
the time the teacher was talking. Learners were reading from the hand outs
and the lesson went well beyond the allocated 1hour and the teacher could
not complete the lesson.
The practical was demonstrated as a group work and only four learners got
involved in the group work and no results were drawn from the practical
demonstration.
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Facilitation of the concepts at macroscopic level:
The educator explained the concept (by reading from the hand out) of the
dissociation of strong acids. She explained the Bronsted - Lowry theory of an
acid – base reaction (by reading from the hand out) by mentioning the
following terms.
• An acid is a proton donor and a base is a proton acceptor.
• The conjugate base of an acid is the ion that remains after the acid has
donated a proton.
• The conjugate acid of a base is the ion that remains after the base has
accepted a proton.
Facilitation of the concepts at microscopic level:
The teacher continued reading from the handouts. She explained that
hydrochloric acid dissociates into H3O+ ions and Cl- ions and acetic acid
dissociates into CH3COOH- ion and H3O+ ions. She also explained that
sodium hydroxide dissociates into Na+ ions and OH- ions. She gave no
further explanations for the reaction.
Facilitation of the concepts at symbolic level:
The teacher once again read the following equation from the hand out.
HCl (aq) + H2O ↔ H3O+ (aq) + Cl- (aq)
CH3COOH (aq)+H2O(l)↔CH3COOH-(aq)+H3O+(aq)
NaOH (S) ↔ Na+ (aq) + OH- (aq)
NH3 (aq) + H2O (l) ↔ NH4+ (aq) + OH- (aq)
Acid → H+ (proton) + Conjugate base
Base + H+ (proton) → Conjugate acid
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Facilitation of the transition from one level to another level:
The teacher engaged learners at the sub-microscopic level by explaining that
an acid-base reaction takes place when protons are transferred. She then
shifted to the symbolic level by using the following equation in explaining the
reaction between sulphuric acid and sodium hydroxide forms sodium sulphate
and water.
H2SO4 (aq) + NaOH (aq)→ Na2SO4 (aq) + H2O(l)
The teacher mentioned that the above is a molecular equation because the
reactants and products are represented by means of molecular formulae. She
explained the above equation by using ions, as given below:
2H+(aq)+SO42-(aq)+ 2Na+ (aq) + 2OH-(aq) → 2Na+(aq) + SO4
2- (aq) + 2H2O(l)
The teacher also mentioned that the sulphate ions (SO42- ) and sodium ions
(2Na+) Ions , on both sides of the equation did not change and by omitting
them the equation could be written as follows:
2H+ (aq) + OH- (aq) → H2O (l)
5.4.2 Lesson observation: Mr Mashigo Mr Mashigo had a class of 40 grade 11 learners and the lesson took place in
a laboratory. The topic for the lesson was acid – base reactions and the
duration for the lesson was 1hour. He used hand outs and the chalk board for
the presentation of the lesson. He started the lesson by testing learners on
their prior knowledge needed for the lesson. Learners in the class were
occasionally participating in the lesson. There were no class work and
assessment programmes but home -work was given to the learners at the end
of the lesson. There was no provision for the review of the concepts taught.
The teacher did not complete the lesson during the allocated time. A group of
learners were invited to join the teacher to demonstrate the experiment.
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Facilitation of the concepts at macroscopic level:
The teacher explained that metals react with acids to form salt and hydrogen.
He further explained that when zinc reacts with hydrochloric acid it forms zinc
chloride and hydrogen. The teacher gave a second example of the reaction
between magnesium and nitric acid. He explained that when magnesium
reacts with nitric acid it forms magnesium nitrate and hydrogen. But the
teacher did not mention about any observable changes that could be noticed
during these reactions at the macroscopic level such as the formation of
hydrogen gas bubbles and the disappearance of the solid zinc powder and
the magnesium ribbon after being used up. However, the teacher
demonstrated the reaction between NaOH solution and hydrochloric acid and
used red and blue litmus papers respectively to test the basicity and the
acidity of the solutions with its colour change. He also used red and blue
litmus papers to test the nature of the solution obtained after the reaction. He
indicated that as the colour of both litmus papers turned purple in the solution,
it was a neutral solution. He explained in general that when an acid reacts
with a metal oxide it forms salt and water.
He further added that an acid and a metal carbonate react to form a salt,
carbon dioxide and water. The teacher indicated that when magnesium
carbonate reacts with sulphuric acid it forms magnesium sulphate, CO2 and
water.
Facilitation of the concept of the microscopic level of representation:
The teacher explained the dissociation process of hydrochloric acid. He
explained that when hydrochloric acid dissociates it forms H+ and Cl+ ions.
Bonds are broken and ions are formed. He explained that when nitric acid
dissociates it forms hydrogen ions and nitrate ions and sulphuric acid
dissociated to form hydrogen ion and sulphate ion. He explained that during
chemical reactions, bonds are broken and new compounds are formed.
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Facilitation of the concept of symbolic level of chemical representation:
The teacher wrote the following equations on the chalkboard and then used
the equations in explaining the formation of the products.
Zn + HCl → ZnCl2 +H2 HCl → H+ + Cl-
H+ Cl
Mg + HNO3 → Mg(NO3)2 + H2
HNO3 → H+ + NO3-
MgO + H2SO4 → MgSO4 + H2O H2SO4 → 2H+ + SO4
- Mg CO3 + H2SO4 → MgSO4 + H2O +CO2 Mg2+ CO3
2- H+ SO42- (bonds are broken)
HCl + NaHCO3 → NaCl + H2O +CO2
Facilitation of the transition from macroscopic ↔to sub-microscopic ↔
symbolic level:
In most of the chemical reactions, the teacher touched on three levels of
chemical representations. The teacher had prepared a solution of sodium
hydroxide by dissolving a certain mass of solid salt in water. The teacher
placed a blue litmus paper in the solution and asked the learners to observe
any colour changes and repeated the same process using a red litmus paper.
He indicated that the red litmus paper changed its colour to blue while the
colour of the red litmus paper remained the same when placed in the alkaline
solution. He repeated the above steps using dilute hydrochloric acid and the
two litmus papers. He then added dilute hydrochloric acid to the sodium
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hydroxide solution slowly and explained the reaction using the following
equation.
NaOH(s) + H2O(l) Na+(aq) + OH-
(aq)
HCl(aq) H+
(aq) + Cl-(aq)
NaOH(aq) + HCl(aq) NaCl(aq) + H2O(aq)
The teacher explained that the above reaction was a neutralisation reaction
and the products were a salt and water
5.4.3 Lesson observation: Mrs Mbele Mrs Mbele organised a grade 11 class of 40 learners in a laboratory to
introduce the concept of oxidation – reduction reactions. The allocated time
for the lesson was 1hour. After testing the previous knowledge, she went on
with her lesson by introducing the topic for the day. She used the resource
materials such as the handouts and the periodic tables to clarify the concepts
to the learners. The first half of the lesson was used by the teacher to explain
concepts and the second half for practical demonstration. There was no class
work, assessment or review of the lesson. Home work was given to the
learners. The lesson went beyond the allocated time and the teacher
struggled to complete the lesson on time. The practical was demonstrated
and the teacher involved four learners to carry out the experiments. However,
the practical did not produce the expected results. Learner participation in the
lesson was nominal and they were passive listeners in the class.
Facilitation of the concepts at the macroscopic level:
The teacher explained the term oxidation number using the element nitrogen
in the ammonium ion. She also explained oxidation as loss of electrons and
reduction as gain of electrons. She defined redox reaction as a reaction in
which both oxidation and reduction takes place. The teacher explained
reducing agent as the compound that is oxidised and the oxidising agent as
the compound that is reduced. The teacher used the reaction between copper
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sulphate and zinc and explained to the learners that the product formed were
white zinc sulphate and copper. The teacher ensured that the learners
observed the changes that took place in the experiment. The teacher
explained that the presence of Cu2+ions in the solution gave the solution a
blue colour. When excess zinc powder was added to the solution, the blue
colour became lighter and disappeared. The teacher indicated that the
cu2+ions were reduced to copper atoms by zinc. The teacher also measured
the temperature of the solution before and after the experiment using a
thermometer and noticed that the temperature of the solution increased as the
reaction between zinc and copper sulphate was an exothermic reaction.
Facilitation of the concepts at the microscopic level:
The teacher used the reaction between copper sulphate and zinc to explain
the concept of microscopic level of chemical representation.Using the
following equation she explained that as zinc lost the electrons it became zinc
ion.
Zn → Zn2+ +2e- (oxidation)
The teacher also explained that copper ions gained electrons and became
copper atoms.
Cu2+ + 2e2+ → Cu (reduction)
Facilitation of the concepts at the symbolic level:
The teacher used the following equation to represent the net reaction that
took place.
CuSO4 + Zn → ZnSO4 + Cu
She used the following equation to explain and represent the total redox
reaction.
Cu2+(aq) + Zn → Zn2+
(aq) + Cu (redox reaction)
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Facilitation of the transition from one level to another:
The teacher used the reaction between zinc and copper sulphate to explain
the transformation from one level to another. The teacher demonstrated the
experiment and explained it using the three levels of chemical representation.
The teacher explained that when excess zinc was added to copper(II)
sulphate solution the blue colour disappeared after the reaction. She
reminded the class that the presence of Cu2+ions gave a blue colour to the
solution and the blue colour disappeared when zinc powder was added to the
solution. She explained that copper (II) ions were reduced to copper atoms by
the zinc. The teacher explained that when each zinc atom went into the
solution, it released two electrons and these electrons were directly
transferred into the copper ion to reduce it to the copper atom. The teacher
used the following equations to explain the transition from one level to
another.
CuSO4(s) +H2O Cu2+(aq) + SO4
2+(aq)
Zn Zn2+(aq) +2e-
Cu2+(aq) + 2e- Cu
Zn + Cu2+(aq) + SO4
2+(aq) ZnSO4(aq) + Cu
5.4.4 Trends in classroom observation All teachers used the lecture and demonstration methods to present their
lessons. Very limited number of learners had the opportunity to actually
participate and carry out the experiments that were demonstrated by the
teachers. Teachers tried to explain the concepts of three levels of chemical
representations using the experiments they demonstrated during the lessons.
Reactions that occurred during the experiments were represented using the
chemical equations. However, the majority of the learners in all the three
lessons could not get a better understanding of the concepts taught as the
teachers did not utilise any effective teaching strategies to facilitate the
learning of the concept of chemical representations at three levels.
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5.5 CONCLUSION In this chapter a qualitative research methodology was used to collect and
analyse data for the second phase of the study. Pre-interview and class
observations were conducted to collect the necessary data. After collecting
the data, it was analysed and interpreted. Analysis of the data revealed that
teachers did not have a deeper understanding of the concepts of the three
levels of chemical representations. Hence they didn’t have a specific strategy
to teach and facilitate these concepts effectively to the learners.
A lack of resources for experiments was pointed out as one of the reasons for
the failure of learner understanding of these concepts. Lack of motivation and
goals in learners, seriously affect the learner performance and their
understanding of the three levels of chemical representations. The inability
and lack of strategies of educators to teach the concept of three levels of
chemical representation has serious implications for the understanding of
concepts and the performance of learners in the matric examination.
Therefore it was evident that educators lacked the skills and knowledge to use
the appropriate teaching strategies to teach the macroscopic, microscopic and
symbolic levels of chemical representations.
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CHAPTER SIX
FINDINGS AND RECOMMENDATIONS
6.1 INTRODUCTION
In chapter 5, data required for the second phase of the research study was
collected and analysed using a qualitative research methodology. In this
phase, pre- interviews and class observations were conducted to gather the
data. The data was analysed and interpreted to study the strategies that were
used by the teachers to teach the concepts of chemical representations at
macroscopic, microscopic and symbolic levels. The teaching strategies that
are used by the teachers have implications for the level of understanding as
well as the performance of learners in answering questions that are related to
macroscopic, microscopic and symbolic levels of chemical representations.
This chapter consists of a brief summary of the whole research study as well
as the findings of the research. Based on these findings recommendations for
further research study are also made.
6.2 OVERVIEW OF THE RESEARCH
The purpose of this research study was to investigate the conceptual
understanding of chemical representations by grade 12 learners. In order to
realize the aim of the study, the following objectives were set:
1. To determine the performance of grade 12 learners in responding to
questions at the macroscopic, sub-microscopic and symbolic levels of
chemical representation.
2. To describe how teachers facilitate learner conceptual understanding at the
macroscopic, sub-microscopic and symbolic levels of chemical
representation.
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In chapter 2, a literature study was carried out to explian the terms and
concepts that are associated with the three levels of chemical representations
namely macroscopic, microscopic and symbolic levels. The research study
was carried out in two phases. Both quantitative and qualitative research
methods were utilized to collect and analyze data.
In addressing the first research question, chapter 4 presented the quantitative
analysis of learner responses in the 2008 matric chemistry paper. In
addressing the second research question in chapter 5, I qualitatively analysed
classroom observation and interview data. Major findings of this research
study are discussed and recommendations are made in chapter 6.
6.3 SUMMARY OF THE IMPORTANT FINDINGS The followings findings are drawn regarding the performance of grade 12
learners in responding to questions at the macroscopic, microscopic and
symbolic levels of chemical representations, and the teacher facilitation of
learner conceptual understanding at the above levels of chemical
representations.
6.3.1 Findings from the analysis of chemistry examination scripts The primary aim of this study was to investigate the conceptual understanding
of chemical representations by grade 12 learners. In order to realize the aim
of the study, the performance of grade 12 learners in responding to questions
at the macroscopic, submicroscopic and symbolic levels of chemical
representation were studied and analysed. From the analysis of CFCR
framework of classification, it was observed that:
• Learners performed very poor in all categories of chemical
representation. According to the CFCR framework, all seventy two
questions in the NSC, chemistry question paper of 2008, were
classified into seven categories as shown in Table 4 2. The percentage
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of marks obtained by learners in each category showed that the
performance was poor in all categories.
• In the first level of categorisation (macroscopic), it was found that
learners scored between 51%-100% for six questions and for four
questions they scored between 0%-10%. The lowest scored question
was 5.7.1 where five hundred learners scored only four marks of a total
1000 marks. The question carried two marks, only one learner had full
marks, 458 learners obtained ‘zero’ marks while 39 learners did not
answer the question. This category scored a standard deviation of
20.64, the lowest percentage scored was 0.4% and the highest
percentage obtained was 68.4 %. The performance of learners at this
level was very poor.
• In the second level of categorisation (sub-microscopic), there were
eight questions of which for three questions learners scored between
0% and 10% while for one question they scored between 51% and
100%, for three questions learners scored between 11%-30% and for
one question they scored between 31%-50%. The standard deviation
for the sub-microscopic category was 18.02, the lowest percentage
scored by learners for a question was 6.0% and the highest scored
percentage was 52.6 % for question 1.3. The performance of learners
at this level was not satisfactory.
• In the third category (symbolic level) there were sixteen questions and
they obtained the lowest marks for question 7.4. For this question
learners obtained only 9.3% of the total marks. Learners scored the
highest marks for question 3.1 for which they obtained 62.2% of the
total marks. For one question they scored between 51%-100% of the
total marks, for six questions they scored between 31%-50% while for
two questions they scored between 0%-10%. The standard deviation
for this category was 15.22.
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• The fourth category (macroscopic ↔ sub-microscopic) had nine
questions of which the highest scored question was 3.4 with a score
percentage of 63.3% and the lowest scored question was 9.4 with a
score percentage of 15.87%.The standard deviation for this category
was 17.232. In this category, there were no questions scored between
0% and 10%. The learner performance was slightly better compared to
the previous three categories.
• The fifth category (macroscopic ↔ symbolic) had only six questions of
which the lowest scored question was 11.4 and the learners obtained
only 13.0% of the total marks, while the highest scored question was
3.2 for which they obtained 70.5% of the total marks. This category had
a standard deviation of 21.10.
• The sixth category (sub-microscopic – symbolic) had eight questions.
The lowest scored question was 12.3.4 and the learners obtained only
3.73% of the total marks allocated and the highest scored question was
11.3 for which they obtained 38.5% of the total marks. The standard
deviation for this category was 11.16. The performance is not better
than other categories.
• The seventh category (macroscopic ↔ sub-microscopic ↔ symbolic)
had only three questions. For question 9.6.1 they scored only 24.8% of
the total marks, question 9.6.2 scored 8.4% and for question 10.2.1
they scored only 15.2% of the total marks for the question. The
standard deviation for this category was 8.24.
• In the overall analysis, the sample of five hundred learners obtained
below 50% marks for sixty questions and for twelve questions they
scored just above the 50%.
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• There is no significant difference in learner performance between the
categories. Learners struggled in all the categories namely
macroscopic, microscopic and symbolic and the mixed categories.
6.3.2 Findings from interviews and class observation of teachers
The second objective of the research study was to identify the strategies that
teachers used in facilitating learner understanding at the macroscopic, sub-
microscopic and symbolic levels of chemical representation. Pre- interviews
and lesson observations were done with three teachers from township
schools. The following are the findings from the data collected during the
interviews and lesson observations with the teachers.
• Although teachers did not explicitly verbalise any conception of the
three levels of chemical representation, the classroom observations
suggested that teachers were facilitating learner understanding to a
certain extent at these levels. With the limited resources, they were
facilitating the concepts at macroscopic level using demonstrations.
• However, due to teachers having a limited conception of the levels of
chemical representation, they were unable to plan strategies that
effectively targeted the facilitation of learner understanding at these
levels.
• There was very little evidence of teachers explicitly helping learners
make the transition from one level of chemical representation to
another. However, all three teachers depended heavily on the pratical
demonstration methods to explain reactions that took place at
macroscopic and sub-microscopic levels. They also utilised the
symbolic level of representations to express the reactions that occurred
at microscopic levels. However, they could not assist the learners to
understand fully the concept of transition from one level to another
level of chemical representation.
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6.4 RECOMMENDATIONS
There are many factors that cause the poor performance of learners in the
grade 12 NSC examination. Lack of resources, non- committed teachers, lack
of professional content knowledge, lack of learner motivation and commitment
and uncertainty in the curriculum planning are some of the factors that
negatively affect the learner performance. In promoting the performance of
learners in chemistry, the following recommendations are made:
• Schools need to be adequately resourced with laboratories containing
chemicals and equipment so that learners can be given the opportunity
to engage at a macroscopic level in chemistry level. This will ensure
that abstract concepts can become more concrete to learners.
Furthermore, the NCS stipulates the development of process skills in
science learners. It is generally accepted that laboratory work
reinforces theory in a practical context. In this process of applying the
theory to practical situations, learners gain a better understanding of
the basic concepts and principles of science (Onwu & Fraser, 2006). At
present, many schools in rural areas, due to the high intake of learners,
converted laboratories into normal classrooms. And as a result, in
those schools, chemicals and equipments are packed away in store
rooms and not used adequately. This situation will need to be
addressed by education officials.
• The Department of Basic Education should initiate in-service courses
for physical sciences teachers in chemistry. This should be done with a
view to developing teacher knowledge and understanding of the levels
of chemical representation to enable them to more explicitly fashion
strategies in facilitating the learning of concepts at these levels.
Teachers need to be suitably qualified and confident in the teaching of
science and in so doing preparing learners for tertiary education
(James, Naidoo & Benson, 2008).
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6.5 SCOPE FOR FURTHER STUDY
In view of the above recommendations it is suggested that perhaps a
professional development programme for teachers in chemistry be developed.
The effectiveness of this programme should then be evaluated against
possible gains made by teachers in facilitating chemistry learning in the
classroom.
6.6 CONCLUSION Conceptual understanding of chemical concepts is greatly related to the
learning of chemistry. Chemistry is unique because of its dual characteristics:
the real and visible characteristics of the macroscopic level and the real and
invisible characteristics of the sub-microscopic level (Treagust &
Chittleborough, 2008). Teacher quality has been widely shown to have a large
impact on learners’ achievement and one aspect of teacher quality is their
content knowledge (Saderholm & Tretter, 2008). According to Chaney (1995)
teacher pedagogical training was important when the focus was on the
content area taught by the teacher.
Therefore, a committed, qualified and innovative human resource is essential
for the effective chemistry curriculum delivery at our schools to improve the
learner performance in the NSC chemistry examination. Poor understanding
of the concepts in chemistry, results in poor performance in the examination.
Therefore, existing staff should be empowered and up skill programs should
be organised to improve the curriculum delivery at schools. Resources which
are essential for the chemistry curriculum delivery should be made available
to all the schools especially in the previously disadvantaged schools.
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APPENDIX A
ETHICAL CLEARANCE
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APPENDIX B
PERMISSION FROM GAUTENG DEPARTMENT OF
EDUCATION (GDE)
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APPENDIX C
LETTER OF CONSENT
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APPENDIX D
NSC CHEMISTRY QUESTION PAPER 2008 PAPER 2
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APPENDIX E
INTERVIEW SCHEDULE
1. Do your learners encounter any difficulties learning chemistry? If so,
please explain. Use examples to explain these difficulties.
2. Why do you believe they encounter these difficulties?
3. Do your learners find it easier learning chemistry or physics? Explain.
4. Do your learners perform better at chemistry or physics?
5. Do learners enjoy learning chemistry to physics? Explain.
6. When teaching chemistry do you teach it differently compared to physics?
Explain.
7. Do you teach all topics in chemistry the same way ? Explain.
8. How do you teach each of the following topics?
8.1 The formation of a covalent bond.
8.2 The formation of precipitates in ion precipitation reactions.
8.3 Writing equations for acid-base reactions.
9. What challenges do you have in teaching chemistry? Explain.
10. Do you prefer teaching chemistry or physics?
11. Do you know what is meant by macroscopic, sub-microscopic and
symbolic representations in chemistry?
12. Do your learners have difficulty with chemistry symbols and chemical
formula? Explain. How do you teach this?
13. Do your learners have difficulty doing chemistry experiment? Explain. How
do you teach this?
14. Do you have difficulty understanding that substances are made of
particles they cannot see? Explain. How do you teach about this?
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APPENDIX F
PRE - INTERVIEW TRANSCRIPTS
F.1: Pre - Interview - Mrs Khumalo Researcher: Good morning Mrs Khumalo. Thank you very much for
coming for the interview and welcome.
Mrs Khumalo: You are welcome.
Researcher: I’m Mrs Joseph, and I’m doing my masters at UJ and this
interview is going to be part of my research. Okay?
Mrs Khumalo: Okay.
Researcher: Thank you very much for being part of my research
project.
Mrs Khumalo: I’m Mrs Khumalo, I’m the head of the department of
science in X Secondary School and then also teaching
physical sciences. Grade 10-12.
Researcher: Okay. If you don’t mind can you explain to me your
qualifications and your teaching experience?
Mrs Khumalo: Okay, I started teaching as a temporary teacher in
Soweto in 1999. Then I got a promotion in 2006 as an
HOD here in Orange Farm Secondary school. Okay, X
Secondary school. I’ve done my, my studies. I did my
Honours degree at WITS university, majoring in physical
sciences and I continued doing my, I did my Honours
again at UJ, this time doing management and leadership.
Researcher: Okay. Which mean you did two Honours?
Mrs Khumalo: Two Honours degrees. Yes.
Researcher: Okay, that’s good. So you know how to manage your
department.
Mrs Khumalo: Yes
Researcher: As well as your subject.
Mrs Khumalo: Yes, my subject.
Researcher: That’s good. Okay, the first question for this interview is:
‘Do your learners encounter any difficulties in learning
164
chemistry? If so, please explain. You can use examples
to explain these difficulties.
Mrs Khumalo: I, I think, I think my learners are encountering lots of
difficulties. For example, in, in chemical change, when
you ask them to write equation, it is difficult for them. To
write the, the word, maybe I give them the word of a
chemical and they must write it in a symbol. It’s very
difficult, they don’t know their symbols. The formulas of,
of the chemicals. They don’t know. So, to know the whole
concept of chemistry without knowing the formulas it’s,
it’s difficult.
Researcher: Okay, can you, can you suggest some, reasons for this
problem?
Mrs Khumalo: I think my learners are not committed.
Researcher: Not committed?
Mrs Khumalo: Yeah, they are not committed.
Researcher: So this problem is coming.
Mrs Khumalo: And they do not practice.
Researcher: Okay. So you say this problem is coming from learners or
what about teachers? Are they also part of this? This
problem?
Mrs Khumalo: No, I’ve never seen the problem with teachers.
Researcher: Okay.
Mrs Khumalo: Mostly learners.
Researcher: Okay.
Mrs Khumalo: Their problem is that they learn something in class, they
do understand it in class but when they go home they
don’t practice.
Researcher: Okay.
Mrs Khumalo: Come tomorrow they know nothing. You have to start
afresh.
Researcher: Okay. So that is the problem that you are encountering?
Mrs Khumalo: Yeah.
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Researcher: Okay. Thank you very much for that one. Second
question is: ‘Why do you believe they encounter these
difficulties? Why?’
Mrs Khumalo: Because whatever they are writing doesn’t make any
sense. When, let’s say they are given some statement
and the formula’s in words they have to write the full
equation it is difficult for them, you see something that is
totally strange. That you have never taught them. So
when you ask them they just take that ok, if let’s say for
example for potassium, if the symbols is potas-, is
potassium, the first letter must be the symbol for that
element. So, I think the practice also it’s, it’s very
important. If they, if they were practicing they won’t
encounter any difficulties. So my learners are lazy.
Researcher: Okay. So next question is: ‘Do your learners find it easier
learning chemistry or physics? Explain.
Mrs Khumalo: I think the chemistry, it’s easier compared to physics.
Researcher: Okay.
Mrs Khumalo: Because what, what I’ve noticed that in physics there are
lots of calculations and the majority of them they don’t like
mathematics.
Researcher: Okay.
Mrs Khumalo: They also don’t understand the formulas, how to use
formulas in physics.
Researcher: Okay, so what you are saying is that they like chemistry?
Mrs Khumalo: They like chemistry but they don’t understand it also.
Researcher: Okay. So that is a very serious problem. And you
previously you said that they have problems…
Mrs Khumalo: Yes.
Researcher: In chemistry?
Mrs Khumalo: They have problems in chemistry but they are better
compared to physics.
Researcher: Physics. Oh, okay. That’s right. Do your learners perform
better in chemistry or physics?
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Mrs Khumalo: I think we’ve answered that again.
Researcher: Do learners enjoy learning chemistry to physics?
Mrs Khumalo: Yes they do enjoy learning chemistry more because of
the practicals. They like to do practicals.
Researcher: Okay. So they like chemistry?
Mrs Khumalo: They like chemistry compared to physics.
Researcher: Which means you don’t do practicals for physics?
Mrs Khumalo: We do practicals for physics but chemistry is something
that they see maybe sometimes colour changing. They,
they like that stuff.
Researcher: Okay. Yeah, next question. When teaching chemistry do
you teach it differently compared to physics?
Mrs Khumalo: Differently? What do you mean by differently?
Researcher: Okay, listen to this question. When teaching chemistry,
do you teach it differently compared to physics?
Mrs Khumalo: I, I think I can say I teach it differently. Because there are
lots of practicals in chemistry. Some of the things if the
learners don’t understand the theory part of it, I have to
do the practical.
Researcher: Okay.
Mrs Khumalo: Ja.
Researcher: So what you are saying is when they find it difficult then
normally you do the practical?
Mrs Khumalo: I do the practical. If they don’t understand, they don’t see
the concept. Why do I say this will combine this two
things to get this. So I decide even if there are no
apparatus I improvise.
Researcher: Okay. Which means is it not better to teach with
practicals? So that they know one can.
Mrs Khumalo: It is better to teach with practicals.
Researcher: Ja.
Mrs Khumalo: Yes.
167
Researcher: Okay, now next question. Do you teach all topics in
chemistry the same way? All sections in chemistry the
same way?
Mrs Khumalo: Yes, if they’re practicals I teach them the same way.
Researcher: All of them? Okay, okay. How do you teach each of the
following topics? First one: The formation of the co-valent
bond.
Mrs Khumalo: Okay, when I teach there about the co-valent bonds I, I
have to make some practicals of some equations you did,
let’s say you want to make, you, you want to have the
product, first thing in your reactants then the bond must
break then that attraction between the elements or
whatever so that the other bond can form.
Researcher: Okay, that’s it. Okay, then you talk about the formation of
ions and all those things? Before the bonds?
Mrs Khumalo: Yeah, we talk about the formation of ions because when,
when it breaks there are ions forming and the ions will
attract each other.
Researcher: Okay.
Mrs Khumalo: Then the positive and the negative ion attracting each
other.
Researcher: Okay, that’s right. Next is the formation of precipitates in
ion precipitation reactions.
Mrs Khumalo: In this one I, I, always like to do the practical part of it so
that the learners can see if we talk about the precipitate,
what do you mean? It makes the truth is they will see that
I am having this and that then when I mix it there be a
precipitate.
Researcher: Can you give me an example for that one?
Mrs Khumalo: I’ve forgotten the example.
Researcher: Okay.
Mrs Khumalo: Because I taught it last in grade 10.
Researcher: Okay. Let’s move to next. Writing equations for acid
based reactions. How do you teach that?
168
Mrs Khumalo: When writing equations I, I, I first teach them there’s a
term dissociation. Whereby when an acid it meets with
something, it dissociates into ions so when these ions are
forming both the acid and the base, the positive will be
attracted to a negative in a base and vice versa so that
you can get the product, the salt and water.
Researcher: Thank you. Okay, that’s it.
Mrs Khumalo: Yeah, but in most cases I, I like to do the practicals in
acid and bases.
Researcher: Okay. Next question. What challenges do you have in
teaching chemistry? Explain. What challenges?
Mrs Khumalo: If I don’t have enough chemicals. Little [Inaudible]
sometimes some of the things you don’t have let’s say in
the boxes. It’s better if, if some of the things I can buy
them. For example the, there was a, practical in rates of
chemical reactions. Where I’ll have, I, I, I have to take out
money and buy the Cal-C-Vita to do the practical so that
learners can see but if there are no chemicals it’s difficult.
Researcher: [Inaudible] can be difficult, but it is the duty of the school
to buy chemicals.
Mrs Khumalo: Yes, the duty of the school…
Researcher: Did you talk to the school?
Mrs Khumalo: But at times we need something, they take their time.
Because it must start from the principal, by SGB before
they can buy anything for it.
Researcher: Do you prefer chemistry than physics?
Mrs Khumalo: Yeah. I, I like chemistry ja, because what I teach it’s
something that I see.
Researcher: Okay.
Mrs Khumalo: Even physics is something that I see.
Researcher: Ja.
Mrs Khumalo: Momentum, everything.
169
Researcher: If you saw it but the, before I like physics, now I enjoy
chemistry more because really I am being discouraged by
the learners.
Researcher: Okay.
Mrs Khumalo: They are failing physics like nobody’s business.
Researcher: Okay.
Mrs Khumalo: Chemistry is much better.
Researcher: Much better. Of physics you see or would it have been
better.
Mrs Khumalo: Yes, everything that is happening.
Researcher: Okay. Chemistry is the problem.
Mrs Khumalo: Ai, I enjoy chemistry very much.
Researcher: Okay, yeah. Do you know what this mean by microscopic,
sub-microscopic and symbolic representations in
chemistry?
Mrs Khumalo: Ah, I know them but I…
Researcher: Can you explain them?
Mrs Khumalo: No I can’t, I cannot get in detail with them but I, I know
them when I’m taking the book and reading and I know
what that thing is.
Researcher: Maybe by little bits because you now said a rate of
reaction, you said you need a [inaudible] bond, a Cal-C-
Vita for a practical isn’t it?
Mrs Khumalo: Yes.
Researcher: Okay, take that example.
Mrs Khumalo: Ja, for example the rate of reaction if you are mixing
some of the things and you are seeing the results that is
microscopic because it is something that you see. Micro
is something that you know it is happening but you
cannot see it through your naked eyes micro. Ja, you
cannot see.
Researcher: Okay, that’s very good. You cannot see, okay. Then
symbolic?
170
Mrs Khumalo: Symbolic when we, when we are combing these things
and write in chemical equations. In rates of chemical
reaction, when you are dealing with symbols like the, the
hydrochloric acid mixing with the sodium hydroxide. So
there will be that dissociation and the symbols will
combine to form the new products. I think that is
symbolic.
Researcher: Okay. That’s it. Do your learners have difficulty with
chemistry symbols and chemical formula? Explain. How
do you teach this one?
Mrs Khumalo: Yes, they have a, a very, very difficult report. As, as I’ve
said at the beginning that when you want them to write
the formula they can come from the anything. It’s difficult
for them, but always when I am teaching it, I always say
to them they must take out the periodic table. They must
know and understand the periodic table. When they
combine the elements they must get something out of
that. They must know the ions of the element…
Researcher: Okay.
Mrs Khumalo: But still they are having difficulties even if I start teaching
them from grade 8. Because some of them I taught them
in grade 8 but..
Researcher: Still they are having problems.
Mrs Khumalo: Ja, they are having problems.
Researcher: Do your learners have difficulty in doing chemistry
experiments? How do you teach this?
Mrs Khumalo: No. they don’t have difficulty as long as they, they have
instructions. But the problem with them, always before I
give them the experiment to do, I give them the
experiment to do, I always ask them to write down the
question. The investigative question and the hypothesis,
they are having problems with that but once they have
everything they can do that practical. They enjoy doing
the chemistry experiment.
171
Researcher: Which means you must give them all the instruction?
Mrs Khumalo: They want to have all the instructions.
Researcher: That is, ja that is where the problem is.
Mrs Khumalo: Yes.
Researcher: Okay. So you give them all the instruction?
Mrs Khumalo: Not always. Not always.
Researcher: Okay, that’s good.
Mrs Khumalo: Okay.
Researcher: ext question. Do you have difficulty in understanding that
substances are made of particles they cannot see.
Explain. How do you teach about this one? Should I
repeat?
Mrs Khumalo: Yes.
Researcher: Do you have difficulty in understanding that substances
are made up of particles that they cannot see, that you
cannot see?
Mrs Khumalo: I, no not as such.
Researcher: Explain how do you teach this one? To the learners?
Mrs Khumalo: I, I, I, I use the equations also here when I teach when I
teach the substances. For example, if I mixed two things
they, they will mix, I like to make an example of water and
oil. Those two do not mix. But when you take water and,
and milk, let’s take the milk, fresh milk if you have water
and they can mix them. The particles will collide and
those particles, we don’t see them, but what we see at
the end is a milky substance in the container. That means
the particles have mixed and collided.
Researcher: Okay. That’s it. Okay, thank you very much. This is the
end of the interview. I thank you very much for your
cooperation.
Mrs Khumalo: Okay, thank you.
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F.2: Pre - Interview - Mr Mashigo Researcher: This pre-interview is conducted by Mrs. Aleyamma
Joseph with Mr Mr Mashigo, who is a teacher at Y
Secondary. Mr Mr Mashigo let us start with this interview
with a short introduction. Let me introduce myself to you.
I’m Mrs Joseph who is a student at UJ, doing Masters in
Science Education. I, I’m here to do this interview
because it’s part of my research. Can you introduce
yourself.
Mr Mashigo: I am NP Mr Mashigo, a teacher at [Inaudible] secondary
school where I am teaching physical science Grade 11
and 12.
Researcher: Okay. Now let me clarify a few things. In this research I
need to do four things. The first of these are, completion
of the questionnaire by the educators, then the educators
they had to attend a pre-interview, then I need to observe
a one hour lesson, then I need to do the post-interview
with the same educators. Okay? Now in this interview I
will ask you fourteen questions and it is strictly about our
curriculum. If any questions aren’t clear when I ask, you
have the freedom to ask me to repeat it. Which I will do it.
Now to guide you through certain aspects while you are
talking maybe I may ask you some follow-up questions.
Then I can guarantee that whatever you say is strictly
confidential. I will treat it as strictly confidential so there is
no need for any fear or anything.
Mr Mashigo: I understand.
Researcher: Okay, thank you very much. Let us start with the
questions. The first question is: ‘Do your learners
encounter any difficulties in learning chemistry?’
Mr Mashigo: No.
Researcher: If so, please explain, use examples to explain these
difficulties’.
173
Mr Mashigo: No, they don’t encounter difficulties. Not at all, but it’s
only that learners don’t exert themselves at all. What I am
trying to say is that now after a lesson they don’t sit down
and read. Sometimes they will wait for one to come to
class so that then they can open up their textbooks.
Researcher: Okay. So which means what you are saying there is no
follow-up?
Mr Mashigo: There is a follow-up by learners…
Researcher: By learners…
Mr Mashigo: …there is no follow up…
Researcher: …there is no follow up…
Mr Mashigo: …they only open the textbook when they, when the
teacher enters the class, the classroom.
Researcher: Okay, okay. Second question is why do you believe they
encounter these difficulties? You said there’s no problem,
isn’t it?
Mr Mashigo: Yes.
Researcher: Okay. But still that’s a problem. When you say that
learners don’t do any follow-up means they don’t do
homework, they don’t read at home, isn’t it?
Mr Mashigo: That is true, particularly to read at home so as to make a
follow-up on the, on the topic that was introduced already.
Researcher: Okay. That’s right. Do your learners find it easier learning
chemistry than physics? Explain.
Mr Mashigo: They find it easier learning chemistry than physics
because with physics there is somehow calculations.
Mathematics is involved, but with chemistry that is when
our, they find it easier to, to understand…
Researcher: Okay.
Mr Mashigo: …because there’s no that mathematical calculations.
Researcher: So these learners are coming from a very poor
background in maths?
Mr Mashigo: Yes.
Researcher: Okay.
174
Mr Mashigo: That is why I know they are running away from science
going for maths actually going for maths lit…
Researcher: Okay.
Mr Mashigo: …and as a result they leave science.
Researcher: So maths lit is a problem now?
Mr Mashigo: Maths lit is a problem because now learners run away
from maths.
Researcher: Okay. Do your learners perform better in chemistry or
physics?
Mr Mashigo: They perform better in chemistry than in physics.
Researcher: Okay. Do learners enjoy learning chemistry to physics?
Mr Mashigo: They do enjoy learning chemistry.
Researcher: When teaching chemistry, do you teach it differently
compared to physics?
Mr Mashigo: I, I teach in the same way but because of the calculation
part of it learners prefer chemistry than physics.
Researcher: Than physics?
Mr Mashigo: Yes.
Researcher: Okay.
Mr Mashigo: We have for instance now when it comes to electricity,
there is those calculations involving Ohm’s law…
Researcher: Okay.
Mr Mashigo: …and then to them is becomes difficult that they don’t
understand the how.
Researcher: Okay. So which means in exam your learners perform
better in chemistry?
Mr Mashigo: There they perform very bad, very good in chemistry.
Researcher: Okay. Do you teach all topics in chemistry the same way?
Explain.
Mr Mashigo: I teach them in the same way, in the sense that now I, I
start first by, looking at their pre-knowledge then build on
that, on each and every topic that I, I handle.
Researcher: Okay. How will you teach each of the following topics:
Now the first one, the formation of co-valent bond.
175
Mr Mashigo: I start first by introducing them to the periodic table. So
that they can understand that now when we say there is a
bond elements from certain particular group can form one
bond, another bond can form double bond, but now when
it comes to co-valent bonding I always tell them that now
there is that sharing of a pair of electrons after
overlapping and then they understand that, I also, in fact,
for them to understand what I normally do, I show them
that now. Stick your hand out and then I, I, I catch a hand
and say: ‘if you don’t let go and I don’t let go it means we
are bonded together…
Researcher: Okay.
Mr Mashigo: …but now if I have more electronic activity than you then
it means your hand will be closer to me than to your body.
Then it means that now we have that overlaying bond
and a that also introduces a electronic activity at the
same time.
Researcher: That’s good. Okay, the formation of precipitates in ion
precipitation reactions.
Mr Mashigo: When I teach that one I start first by performing a
practical investigation now.
Researcher: Okay.
Mr Mashigo: Like for instance now, I will show them say copper
sulphate and then, double hydrogen sulphide. They will
see that there will be something that settles down at the
bottom.
Researcher: Okay.
Mr Mashigo: Then I start from then say that now in, in some reactions
you find that now there is something that comes out of
the solution, what we call a precipitate. Then they’ll
understand that now all from the practical investigation it
means we have a solution but when something comes
out then I know it’s a precipitation and it is easier for them
176
when I do say for instance now, a solution and then on
that solution I add say it’s a solution, then I add a, a salt…
Researcher: Okay.
Mr Mashigo: ….then they realise that now at the bottom of the
container there is something that forms, then they
understand that that is now a precipitate and that also
teaches them the common ion effect.
Researcher: Okay. Then a how do you explain the formation of that
precipitate?
Mr Mashigo: I explain that formation of that precipitate in terms of the
reactivity of some elements or ions.
Researcher: Okay. So the formation of ions and everything you don’t
explain there? In the solution?
Mr Mashigo: No, I do explain.
Researcher: You explain?
Mr Mashigo: Yes.
Research: How do you explain that?
Mr Mashigo: I, I first of all tell them that some substances are more
reactive than others. In the sense that now when you add
one substance in a solution of one another, then the other
substance will be kicked out from the solution and settle
at the bottom. I make an example about the group 7 the
hal-, the halogens. That if chlorine is added to a solution
of potassium bromide then because chlorine is more
reactive than bromine then bromine will settle at the
bottom.
Researcher: Okay, that’s right, now writing equations for acid based
reactions. How do you explain that? Or how do you
teach?
Mr Mashigo: How do I teach acid based reactions?
Researcher: Yeah. Writing, how do you write? How do you teach the
way how to write equations for acid based reactions?
Mr Mashigo: The first thing that I, I start with, I show, show them the
formula of acids and bases and then I teach them that
177
now for reaction to occur all bonds are broken and new
bonds are formed. And then, I then go onto tell them that
now with an acid when all bonds are broken, you have
those hydrogen protons and then this hydrogen protons
can be [Inaudible] this hydrogen protons can be
transferred to some other substances and then those
substances will be then the bases. And then again I show
them that now when an acid react with a base the al-,
they’ll always be a salt and a, a salt and water. Then I, I
go back again and show them that now how is that water
formed from that hydrogen that at a, acid is giving away
and combines with oxygen from a base and then form
water and how a salt is formed. Is that now, say for
example now I’m looking at an acid reacting with a
carbonate then I show them that now from the acid you
have that hydrogen you have say for instance it’s
hydrochloric acid. You’ll have hydrogen and a chloride ion
and then from a carbonate then you’ll have say for
instance now it was sodium carbonate, then you’ll have
that sodium and then I tell them from one substance one
with a positive ion will combine with the one with a
negative ion from the other substance. Then I show them
how they combine and then I explain that now from, from
a, from that CO3 that is where now one oxygen will come
out and combine with that hydrogen from an acid of warm
water. And then what is left now? Then I ask them: from if
I take away one oxygen atom, what is left? And they will
know that now it will be carbon dioxide and then they now
understand that now. How that acid and that base
reacted.
Researcher: Okay. Ja, that’s right. Next question, what challenges do
you have in teaching chemistry? Explain.
178
Mr Mashigo: In teaching chemistry, like I mentioned earlier that my
learners don’t encounter problems but that they don’t
exert themselves. I don’t have that challenges.
Researcher: Okay.
Mr Mashigo: I really do not have challenges.
Researcher: Okay. That’s right. Then do you prefer teaching chemistry
or physics?
Mr Mashigo: I prefer to teach physics and chem., both of them. The
reason being that now I think I’m more knowledgeable on
both of them.
Researcher: Okay. That’s good. Do you know what is meant by
microscopic, sub-microscopic and symbolic
representations in chemistry?
Mr Mashigo: Come again, you said?
Researcher: Do you know what is meant by microscopic, sub-
microscopic and symbolic representations in chemistry?
Mr Mashigo: With that I am not sure about, but what I understand
about macro is that it’s a something that can be
seen…but now when it comes to sub-micro I don’t know
whether we mean, microscopic reaction or something.
Researcher: Okay. The word is microscopic, yeah. So otherwise you
don’t know anything more than that?
Mr Mashigo: No.
Researcher: Symbolic representations?
Mr Mashigo: That is what, that is what I, I, I’m not clear about.
Researcher: Okay, symbolic?
Mr Mashigo: Yes
Researcher: Okay.
Mr Mashigo: Or does that mean a symbol of or now it becomes clear
to me Ja, I can benefit, sorry. I can be in a position to
show them how to the symbols of different substances
are written and all that.
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Researcher: Okay. Do your learners have difficulty with chemistry
symbols and chemical formula? Explain how will you
teach this?
Mr Mashigo: They don’t have a problem as far as I know.
Researcher: Is it? Okay, so you are happy that all the learners they
know chemistry very well. That is what you are saying?
Mr Mashigo: What I am saying is that now they know chemistry very
well.
Researcher: Okay. Do your learners have difficulty in doing chemistry
experiments? Explain how do you teach this?
Mr Mashigo: They don’t have a problem in doing, experi-, in
performing experiment, chemistry experiments. But what I
realise is that now I need, I always guide them by giving
them worksheets that shows, how to go about and then
they themselves can be in a position to identify variables
and all that…
Researcher: Okay.
Mr Mashigo: …although somewhere I need to guide them towards
some variables.
Researcher: Okay. So which means with the, your guidance they
perform their experiments better.
Mr Mashigo: Yeah.
Researcher: Okay. That’s right. Do you have difficulty in understanding
that substances are made of both particles that they
cannot see? Let me repeat the question. Do you have
difficulty understanding that substances are made of both
particles that they cannot see? Explain how do you teach
about this one?
Mr Mashigo: No I don’t have difficulty with the, with that because the
first thing that I know they know, is that now they cannot
see an ion atoms but they can see some substances and
I, I sometimes refer them to physics. Where now in, in
electricity they hold, conductor and they could feel that
now there is something moving and when I cut it across
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they can see they cannot see what is it that is moving, but
I don’t cut it while the switch is on.
Researcher: Okay.
Mr Mashigo: I don’t, I don’t have a difficulty with that.
Researcher: Okay, that’s right. So that is the end of our interview. Do
you have any comments?
Mr Mashigo: No I don’t, not at all…
Researcher: Not at all.
Mr Mashigo: Because I did understand every question although I did
have a difficulty in one or two questions.
Researcher: Yeah, so Mr. Mr Mashigo thank you very much for
participating in this interview…
Mr Mashigo: It’s my pleasure
Researcher: Thank you.
181
F.3: Pre - Interview - Mrs Mbele Researcher: Good morning Mrs. Mbele.
Mrs Mbele: Good morning.
Researcher: I am doing a Masters degree at the University of
Johannesburg in science education and I have to do a
mini dissertation for my research.
Mrs Mbele: Okay.
Researcher: Now the topic for this one is the chemical
representations. Now for this research there are three
steps involved. One, filling the questionnaire, second one,
the pre-interview…
Mrs Mbele: Pre-interview…
Researcher: which we want to do now. Third will be the class
observation…
Mrs Mbele: Class observation…
Researcher: Okay?
Mrs Mbele: Okay.
Researcher: Those are the steps involved. Now let us start with our
interview. Let us introduce ourselves. Let me do it first.
I’m Mrs Joseph and also I am a student at the University
of Johannesburg doing my masters…
Mrs Mbele: Okay.
Researcher: …and I am working on a dissertation in the subject of
physical science. Okay? Can you please introduce
yourself?
Mrs Mbele: Okay, I’m Mrs Mbele Makoda, I’m a physical science
educator at Z Secondary school. I’m also a deputy
principal at Z Secondary school in Orange Farm.
Researcher: Okay. Do you mind to tell me about your qualifications?
Mrs Mbele: Okay. I’ve done secondary teachers diploma with
Sebokeng college of education majoring in physical
science and life sciences. And then I’ve done also,
management, further diploma in management whereby
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I’ve obtained also my honours in management,
educational management, law and systems through
Potchefstroom University.
Researcher: Thank you. Okay, then can you tell me about your
teaching experience?
Mrs Mbele: Okay. I started teaching in 1999 up until today I’ve never
break any service.
Researcher: Okay.
Mrs Mbele: Yes.
Researcher: And the whole way you were teaching physical science?
Mrs Mbele: Yes. I started teaching physical science in 1999.
Researcher: And even at your first positions as deputy principal still
you teach physical science?
Mrs Mbele: Yes, I’m still teaching physical science.
Researcher: Okay. I can see you are a dedicated teacher.
Mrs Mbele: Yes I am.
Researcher: Okay. The first question is: “Do your learners encounter
any difficulties in learning chemistry? If so, please
explain, use examples to explain these difficulties.”
Mrs Mbele: What I can say is that my learners they don’t experience
any difficulty in learning physical science, especially
chemistry because they find chemistry being easy that’s
what they, their view because they will always tell me that
the physics part is difficult because it has so many
equations, then in chemistry there is few equations and
then you do it practically. You see it practically, what is
happening.
Researcher: Okay.
Mrs Mbele: Yes.
Researcher: Okay, which means they don’t have any problem, you’re
learners are not facing with any problems.
Mrs Mbele: No, in chemistry they’re not…
Researcher: Not?
Mrs Mbele: No, they are facing it in physics.
183
Researcher: Second question is: “What do, why do you believe they
encounter these difficulties?”. That was the question I
was supposed to ask…
Mrs Mbele: Okay.
Researcher: …because you say they don’t encounter any difficulties…
Mrs Mbele: Difficulties, especially in grade 12 they don’t, they were
encountering it in grade 11. It’s only now that they realise
that chemistry is easy.
Researcher: Okay.
Researcher: Can you explain that one?
Mrs Mbele: You know, in, in lower grades you find that schools they
give educators who are not experienced to teach. So
teachers will teach where they understand, especially in
chemistry. Chemistry I can say it’s, I can say most
teachers they fear it because you will find learners saying
in grade 12, we’ve never been taught chemistry in grade
10 and grade 11. Without that chemistry is difficult
because that is what with our teachers we’re saying to us
but when I teach them in grade 12, they, they enjoy it
more than physics. Yeah.
Researcher: Do your learners find it easier learning chemistry or
physics? Explain.
Mrs Mbele: They find it, chemistry easier, ja.
Mrs Mbele: What, what I’ve, I’ve discovered is that in, in physics they
are afraid of these many equations. So because of
maths, maths is also having so many equations. So they
normally relate physics to math and because of their poor
performance in maths it also affect their performance in
physics.
Researcher: Physics?
Mrs Mbele: Yes.
Researcher: So what you are saying, you’re saying in chemistry there
is no need for them to use maths?
184
Mrs Mbele: I’m not saying that in chemistry it’s not, it’s not maths
bound like physics In physics you will find that take for
equations of motion. So they know that if maybe the first
question you’ve, you are wrong in the first question, you
can’t get the second question right. But in chemistry it’s
just straight. Yes.
Researcher: Okay.
Mrs Mbele: Ja.
Researcher: So you are happy with it?
Mrs Mbele: Yes.
Researcher: Okay. Do your learners perform better in chemistry or
physics?
Mrs Mbele: They perform better in chemistry.
Researcher: Meaning all your learners are passing chemistry?
Mrs Mbele: I cannot say all of them. As I am saying that they, they,
there are those who I can say it’s 50/5. I can say
compared to the results of June. It’s 50/50.
Researcher: Okay.
Mrs Mbele: So for the results of final because you can’t see them.
Researcher: Okay.
Mrs Mbele: Yes.
Researcher: Do your learners enjoy learning chemistry to physics?
Mrs Mbele: Yes they do.
Researcher: Can you explain?
Mrs Mbele: As I’m saying…
Researcher: How they feel that…
Mrs Mbele: They, they, they find that chemistry is easy especially
even if they do the practicals because if you say in
chemistry if you say this and this will give this. Take
colour changes all those thing, those are the things that
they see when they do the practical’s. So hence they are
enjoying it.
Researcher: Okay.
185
Mrs Mbele: And even a laboratory to them they will tell you that
they’ve never been to a laboratory. They only entered the
laboratory when they are in grade 12. Hence I said that I
wanted to be given the lower classes based on the
experience that I have.
Researcher: Why do you do that with your learners? When they are in
grade 10 and 11, don’t you allow them to do practical’s in
the laboratory?
Mrs Mbele: It’s not that I don’t allow them. Hence I’m saying that I’ve
been giving the grade 12, I’ve been teaching the grade 12
so the problem that I’ve seen, hence I’ve said that I want
to go to the lower classes. So that the learners they
should be familiar to using the laboratory not to go to the
laboratory when they are doing grade 12 because they,
that is the, that is the problem I’ve encountered. That, the
problem is that learners have never been exposed to a
laboratory. They are, they only go there in grade 12 and
they will ask you: ‘Oh ma’am, what is this?’ You know,
some of the things they are not familiar with them.
Researcher: So which means if you have a chance you want to move
to the lower grades?
Mrs Mbele: Hence I, I’ve done it…
Researcher: Grade 10 and 11?
Mrs Mbele: Ja, I’ve done that.
Researcher: Okay.
Mrs Mbele: After that with the grade 10, now I’ve moved with them to
grade 11.
Researcher: Grade 11.
Mrs Mbele: Next year I will be teaching them grade 12.
Researcher: Is it?
Mrs Mbele: Yes.
Researcher: So you are happy like that?
Mrs Mbele: Yes I’m happy.
Researcher: Okay.
186
Mrs Mbele: Yes I am.
Researcher: Your learners are also enjoying it?
Mrs Mbele: Yes, yes they are.
Researcher: Yeah, that’s good.
Mrs Mbele: Hence I am saying the grade 11’s because you know I’ve
taught them last year. They’ve done the practicals last
year so it’s not something which is new to them in grade
11.
Researcher: Okay. When teaching chemistry, do you teach it
differently compared to physics?
Mrs Mbele: I can say that I, I, I’ve discovered that I’m teaching
chemistry, I’m, because I am enjoying chemistry so
hence I, I’ve discussed with one educator who is also
enjoy physics that we should share. He taught physics
and then I teach chemisty in all the grade 12’s.
Researcher: Is it?
Mrs Mbele: Yes it is.
Researcher: And how was that result?
Mrs Mbele: The results hence I’m saying that we’ve started it this
year.
Researcher: Okay.
Mrs Mbele: So because we are still the learners wrote it on the 20th
so when we are open that’s when we are going to discuss
the results. How was the performance? Then we will
compare the performance between physics and
chemistry. Yes.
Researcher: Okay. So you will let me know?
Mrs Mbele: Yes, I will let you know.
Researcher: Okay. Do you teach all topics in chemistry the same way?
Or differently?
Mrs Mbele: You know when teaching chemistry some of the, the
topics you, you need to use different styles in teaching.
You can’t teach learners the same way because it will
bore them. You, you need to teach them differently. Yes.
187
Researcher: Okay. So you’d use, different methods?
Mrs Mbele: Different methods, ja.
Researcher: Can you explain the methods that you use more
elaborate?
Mrs Mbele: Okay. Take for an example, if you teach batteries, you
have to bring the different types of batteries. Like I have a
car, take learners to your car and explain to them what
type of a battery is this one. Take the batteries of the
remote controls, the torch and just classify the batteries to
them and when you teach, take for example rate of
reaction. It’s different from batteries. When you teach
redox you must explain to them, which one undergoes
what. You know? Before, before explaining to them
chemically you need to do that.
Researcher: Ja.
Mrs Mbele: Yes.
Researcher: How do you teach each of the following topics?
Mrs Mbele: As I‘ve said that’s in batteries you take different batteries
you, you just, you can ask learners what do you think is it
in this battery? They will tell you that in a car battery there
is acid and then a torch battery they will tell you
something that is black when you cut it you find it. Then
you explain to them that now because you have classified
this, this is a secondary battery, this is a primary battery.
So you, you just bring them, you, you, you involve them.
They must explain to you what, what is the difference
between the batteries. Then you push them to say that
okay this is a type of a battery, this is a type of a battery
because you’ve said that in this you find this. This shows
that this one can be rechargeable. This one if it’s dead its
dead, you can’t recharge it. Yes.
Researcher: Now the formation of a co-valent bond? How do you
teach the formation of a co-valent bond?
188
Mrs Mbele: Of a co-valent bond. Okay, you, you start by explaining to
learners what type of a bond, do you get in, in gasses,
you know? If you have carbon and oxygen what type of a
bond is found there? You, you explain to them and then
you explain how is the co-valent bond formed, starting
from what type of a bond is found between this and this.
That’s how I explain it to them.
Researcher: Now, how do teach the formation of precipitates in ion
precipitation reactions?
Mrs Mbele: Precipitation reactions? You know this, of precipitation
reactions I want to be honest with you. I normally ask my
colleague to explain it because I find it difficult for me to
explain to, to learners, but I, I try to explain to them that a
precipitate it’s something that you, you normally found.
Take if you combine two chemicals but it from my,
experience, I have discovered that they don’t understand
it. Hence I normally involve my colleague to come in and
help me in that.
Researcher: So another teacher will come and explain that to them?
Mrs Mbele: And explain it to the learners because I find it maybe
difficult for me to explain to the learners. Hence I’m
saying that we are doing team teaching.
Researcher: Okay.
Mrs Mbele: Yes.
Researcher: Okay, how do you teach about writing equations for acid
base reactions?
Mrs Mbele: Okay, for acid base reactions, what I, I normally do, I start
with the conjugates. The conjugate they should know the
conjugate that if this is an acid immediately when,
because they must know that an acid and a base which
one donates, which one gain an electron. I start there
with them. Then if you write the other one, if it has lost an
electron, so they should know that it is the conjugate of
189
that one which on the left hand side, I normally do that to
them. That’s how I teach them on how to write it.
Researcher: And you use the data sheets also?
Mrs Mbele: Yes.
Researcher: Okay what challenges do you have in teaching
chemistry? What challenges?
Mrs Mbele: What challenges?
Researcher: What challenges you have teaching chemistry?
Mrs Mbele: The challenges are that the equipment, the equipment
because the schools are, are poorly resourced. Because
sometimes if you, you want to do an experiment you have
to go in your pocket to do that. Yes.
Researcher: Is this happening always at your school?
Mrs Mbele: Hai, I can say always because if take for an example you
want to do a gas burner ne? We don’t have gas, you
have to buy a spirits, so to do a burner. From your
pocket. Because we are struggling to get help.
Researcher: So the school doesn’t allocate money? To buy resources
for the learners?
Mrs Mbele: For the lab, no.
Researcher: Okay. Do you prefer teaching chemistry or physics?
Mrs Mbele: I prefer chemistry.
Researcher: Reason?
Mrs Mbele: The reason? I think because I’ve majored with, life
science and chemistry. So both of them they deal with,
chemicals. So the thing that, the last time I did
mathematics was in grade, 12. I think it contributed
because of my major subjects. Yes, because in life
science you do experiment, you see? Even in chemistry
it’s, it’s experiment and challenged.
Researcher: So what about if you are asked to teach physics?
Mrs Mbele: I can teach, I can teach physics, but I enjoy teaching
chemistry. Yes.
190
Researcher: Okay. Do you know what is meant by macroscopic, sub-
microscopic and symbolic representations in chemistry?
Mrs Mbele: No, I can’t. what is that? Macro, sub-micro. Hai, I forgot
these things, in chemistry. Macro, sub-micro and
symbolic. Hai, I forgot that.
Researcher: So you could, you don’t remember anything? But you
enjoy teaching chemistry?
Mrs Mbele: It’s not that I, I won’t remember teaching anything. I won’t
remember, it’s just that I forgot it. Macro, sub-microscopic
and symbolic. You know some of the things they just
move out. It’s not the first time…
Researcher: Okay.
Mrs Mbele: Yes.
Researcher: But, let me ask you this one. Now you teach X learners
chemistry, sometimes you show them experiments,
sometimes they do the experiments.
Mrs Mbele: They do the experiments.
Researcher: Sometimes you demonstrate your experiments. So
regarding those experiments you can’t tell me what is
meant by macroscopic, micro-, sub-microscopic and
symbolic?
Mrs Mbele: Symbolic representation, yes it’s like so Yo! Come on.
Macroscopic, sub-micro and symbolic. I think symbolic
representation this, that’s when you, you give learners
and then whatever they are going to do, they are going
to, to see it practically. Sub-microscopic, microscopic, ja.
You know I just forgot this and…
Researcher: Okay.
Mrs Mbele: I remember you once said it to us, Ja.
Researcher: Now let me ask you then the next question. Do your
learners have difficulty with chemistry symbols and the
chemical formula? Explain how do you teach this one.
Mrs Mbele: Okay. The manner in which I teach them. I normally have,
a periodic table. A periodic table whereby it will have the
191
symbol and the name under it, because you’ll find some
of the, the symbol, they are not, you find some of the
elements in the periodic table they are not the same as
the, like take for an example lead. Lead, the symbol is Pb
but the manner in which you write it is lead. So I normally
tell them that it’s not always going to be the first letter of
the symbol like in oxygen you have O and then the word
will be oxygen. They should Na-know them, especially
the first twenty elements. Those are the elements that
they should know and then the other thing is that when
you teach them in a periodic table. They should know
where are the gasses situated, where are the metals
situated, where are the non-metals situated. Then it
becomes easier for them to remember that okay, if you
say oxygen, oxygen is a gas because sometimes I, I
normally teach them, where is this found. If it is found in
the atmosphere therefore it is a gas. If it’s just found.
Then if it is the metal where, where? So metal you
normally find them in mining. That’s where I normally tell
them. If it is a metal it’s found in mining. So if it’s a non-
metal it can occur everywhere. That’s how I teach that.
Yes.
Researcher: Okay. So do they have difficulties in learning symbols and
chemical formula?
Mrs Mbele: No.
Researcher: No?
Mrs Mbele: They don’t, because what I’ve realised is that they, they
normally start doing that in grade 9. Ja, especially the first
twenty symbols. They like, they, they can even sing them
for you.
Researcher: Oh!
Mrs Mbele: Ja, that’s how I’ve realised it.
Researcher: Okay.
Mrs Mbele: Yes.
192
Researcher: Yes, that’s good. Okay, do your learners have difficulty in
doing chemistry experiments? Explain, how do teach
this?
Mrs Mbele: You know at first, like starting, they will become afraid of
touching, as I was, I’ve, I’ve said that you find them that
it’s the first time they go to the laboratory but when they
see you demonstrating so they, they become interested
in also doing it.
Researcher: Good.
Mrs Mbele: I, I normally say that I’m a normal person like you. If I can
do it, tell yourself that if ma’am can do it, I can also do it.
Yes. That’s, that’s how I teach them.
Researcher: Okay.
Mrs Mbele: That they should have confidence in whatever they are
doing. Yes.
Researcher: Do you have difficulty in understanding that substances
are made up of particles that they cannot see?
Mrs Mbele: Do I have difficulty in understanding that?
Researcher: Explain how do you teach this concept?
Mrs Mbele: That particles?
Researcher: Okay, let me repeat. Do you have difficulty in
understanding that substances?
Mrs Mbele: That substances?
Researcher: Are made up of particles?
Mrs Mbele: They cannot see.
Researcher: That they cannot see. Explain?
Mrs Mbele: Ja, because like take for an example, if you say to them
hydrogen and oxygen they give you water they will ask
you how because the two are the gasses. How, how can
they make water? Well that’s it, I normally say to them
when they combine, hence at first they were the elements
but when they combine they becomes a molecule which
is called water but i-i-it becomes difficult for them to
understand how do? Because these are the two gasses.
193
The combination of them will give us water that’s where
I’ve, I’ve encountered.
Researcher: Okay.
Mrs Mbele: So I normally answer, I, I normally explain to them that
when they are single, they are then elements but the
combination of them they change, they make now to a
compound which is called water. That’s how I do it.
Researcher: Okay.
Mrs Mbele: To them, yes.
Researcher: So then really what you are saying you like to teach
chemistry, your learners also enjoy learning chemistry.
Mrs Mbele: Ja, they enjoy it.
Researcher: Okay.
Mrs Mbele: Ja, hence I’ve said that I, I’ve experienced that with the
group that I’ve started at group, at grade 10. Now they
are at grade 11. They will even ask me ma’am, when are
we going to start with chemistry? And then I said no we,
we are going according to the work schedule We’ll do
chemistry, don’t worry.
Researcher: So you always demonstrate?
Mrs Mbele: I, I always demonstrate to them ja.
Researcher: That’s a good practice. I wish you all the best. Do you
have any questions to ask?
Mrs Mbele: Now, I’m worried about this question. Number 11, hai, it
just went out of my mind. I don’t know but anyway, no
questions.
194
APPENDIX G
LESSON OBSERVATION TRANSCRIPTS
G.1: Lesson Observation - Mrs Khumalo Researcher: This is X Secondary school. I am here to observe Mrs
Khumalo’s lesson.
Mrs Khumalo: Good afternoon class.
Class: Good Afternoon.
Mrs Khumalo: Ja, today we are going to have a lesson on chemical
change. So I am going to give you handouts. Then all the
notes are written there and there are some activities. So
you have to go through all the notes and if there is
something that you don’t understand you have to ask a
question. Is it clear?
Class: Yes.
Mrs Khumalo: Okay, on the chemical change we are going to talk about
the acids and bases and also redox reaction. I hope that
you are familiar with those two sections.
[Hands out notes]
Mrs Khumalo: Okay here are notes.
[Continues handing out notes]
Mrs Khumalo: Okay, I think everyone has his or her own copy now.
Class: Yes.
Mrs Khumalo: We start from page one.
[Opens notes at page one]
Mrs Khumalo: Looking [Inaudible]
Mrs Khumalo: Okay, in our very first page we are having the types of
chemical reactions. Acids and bases, the common acids
and the common bases. Of which those common acids
and bases we learned about them while we were doing
grade eight, grade nine and grade ten. So we are having
the hydrochloric acid, you are familiar with that. I am
195
having here the hydrochloric acid. It’s like water but it’s
not water, its hydrochloric acid. The different types of
acid, we are also having the acids that we are always
using at home. Those types of acids, who, who can give
me an example of that type of acid?
Learner: [Inaudible] the amino acid…
Mrs Khumalo: The?
Learner: The [Inaudible] acid…
Mrs Khumalo: The acid. I am talking about the acids here.
Learner: Amino acid.
Mrs Khumalo: No. Who can help here? The domestic acids. We learnt
about this in grade eight. The domestic acids, the acids
we are always using at home.
Learner: Isn’t it like vinegar ma’am?
Mrs Khumalo: The vinegar. Another example?
Learner: Battery.
Mrs Khumalo: The battery?
Learner: Bleach.
Mrs Khumalo: No, no, the bleach is not an acid. Another example?
Learner: Hydrochloric acid?
Mrs Khumalo: The domestic acids. I am not talking about the laboratory
acids. There’s a difference between the laboratory acids
and the domestic acids. Give an example, one example,
the last example for the domestic acid.
[Silence]
Mrs Khumalo: Tshepo?
Tshepo: Sulphuric acid.
Mrs Khumalo: That is the laboratory acid. I want the name of an acid
that you are always using at home.
Learner: Hydrochloric acid.
[Silence]
Mrs Khumalo: Class I am talking about the things that taste sour and we
are using those things in our homes. The hydrochloric
196
acid you will find it here in the lab. You won’t find it in your
kitchen.
[Silence]
Mrs Khumalo: We had one which is the vinegar. The second one?
[Silence]
Mrs Khumalo: Don’t you know the second one?
Learner: [Inaudible]
Mrs Khumalo: What about … Okay?
Learner: The lemon juice?
Mrs Khumalo: The lemon. The lemon is acidic [Inaudible]. When you
test it you put an indicator in the lemon, the colour will be
an acid colour. Okay, domestic bases?
[Silence]
Mrs Khumalo: We are having laboratory bases here. Okay, give me an
example of a domestic base.
[Silence]
Mrs Khumalo: Kgotatso?
Kgotatso: Bicarbonate?
Mrs Khumalo: Bicarbonate of soda. Anyone?
[Silence]
Mrs Khumalo: The bases that we are using at home?
Learner: Ammonia?
Mrs Khumalo: Ammonia. Where do we get ammonia? In which
substances that we are using at home?
Learner: Cleaners?
Mrs Khumalo: Handy Andy. Okay, so in the first page we are having
different types of acids. You must know them; you must
be familiar with them. Know their names, know their
formulas. They are very important. Is it clear?
Class: Yes.
Mrs Khumalo: Especially when we are doing the reactions on acids and
bases. Okay, then we are having the strong acids and the
weak acids. Looking at the strong acid. Strong acids are
covalent molecules. When an acid is added to water the
197
acid react to the water to form a positive and negative
ions. The process is called ionisation. You take the
hydrochloric acid; remember in grade eight we diluted
hydrochloric acid? If it is too concentrated you have to
dilute it before you use it. Is it clear?
Class: Yes.
Mrs Khumalo: When you dilute hydrochloric acid you have to add some
water in the acid. You know how to dilute an acid
[Inaudible]?
Class: Yes.
Mrs Khumalo: So you have to add water in the acid. Then the ions will
separate. For example, here…
[Moves to write on blackboard]
Mrs Khumalo: …you are having a strong hydrochloric acid. When you
add water here we are going to have two types of ions.
The positive ion and the negative ion. The positive
hydrogen and the negative chlorine. So we call that
process ionisation. So we are having an example here of
an equation. The hydrochloric acid plus water gives us
hydronium ion plus chlorine ion and when you are writing
the equation, you must show the state of that equation. It
must be either a gas, liquid or aqua solution. Is it clear?
Class: Yes.
Mrs Khumalo: Don’t forget to write that. And a weak acid, a weak acid
ionises only partially but a strong acid ionise, ionises
almost completely. So, a weak acid is an acid that has
been diluted. It doesn’t need to be diluted. Is it clear?
Class: Yes.
Mrs Khumalo: it’s like when you are buying the Oros juice at, at the
shop. When you buy the Oros juice in a container it is
concentrated. You need to add water so that you can
drink that Oros juice. But the small bottles of Oros juice
which are written ready to drink, that Oros juice, it’s
diluted. You don’t have to add water. Is it clear?
198
Class: Yes.
Mrs Khumalo: So, an Oros juice which needs to be diluted it’s like a
strong acid.
Class: Yes.
Mrs Khumalo: The one which needs, which don’t need to be diluted is
like a weak acid. So same applies with the bases here.
When a base is dissolved in water the ion break loose.
So through the process called dissociation. So you take
the hydrog-, hydro-, sodium hydroxide, you add water to
sodium hydroxide, you are going to get two ions. The
positive ion and the negative ion. When a base
dissociates or an acid ionises it forms an, an aqua
solution. It is no longer a liquid or a solid. Is it clear?
Class: Yes.
Mrs Khumalo: So, when it, it is mixed with water an aqua solution is
formed. A strong base dissociate nearly completely but a
weak base dissociate partially. Is it clear so far?
Class: Yes.
Mrs Khumalo: Do you have any question in that portion?
[Silence]
Mrs Khumalo: Any question?
[Silence]
Mrs Khumalo: No? Okay, let’s continue. I will ask you questions then
you will have to answer me because it seemed as if you
do understand everything. The Bronsted-Lowry theory of
an acid and a base. According to Bronsted-Lowry theory.
Bronsted-Lowry was a scientist. This scientist said to us
an acid donates a proton. If let’s say for example, I give
you something, what are you going to do?
Class: We are going to take it.
Mrs Khumalo: We have to accept it.
Class: Yes.
Mrs Khumalo: When an acid donates a base must …?
Class: Accept.
199
Mrs Khumalo: Accept it. So, according to Bronsted-Lowry’s theory an
acid is a proton donor which means it gives us the
hydrogen ion and the base is a proton acceptor. It takes
that hydrogen ion. Is it clear?
Class: Yes.
Mrs Khumalo: So, under this, this theory you are having the pairs, the
acid-base pairs. You call them the conjugate acid-base
pair. So the conjugate base of an acid is the ion that
remains after the acid has donated a proton. For
example, we are having the acid like hydrochloric acid,
sulphuric acid, anyone. So when a hydrogen ion is being
donated to the, to the, to the base, then we will be having
the conjugate base. The ion that will be left. Is it clear?
Class: Yes.
Mrs Khumalo: Coming to the conjugate acid of a base. The conjugate
acid of a base is the ion that remains after the base have,
has accepted the proton. The acid will give a proton to
the base and the base must accept. After the base has
accepted the proton there will be that ion that will be left.
That is the conjugate base. The conjugate acid of a base.
Then in this equation we are having a base, it can be
sodium hydroxide, potassium hydroxide, any base you
can think of, plus the hydrogen ion. Then you will be left
with the conjugate acid of the base. So in conjugate acid-
base pairs we have to write the equation on conjugate
acid-base pairs. So before we write the equation let’s look
at proteolysis. Proteolysis is the acid-base reaction where
proton transfer takes place. A conjugate acid-base pair
from, form during proteolysis. In general we are having
the two half reactions. We, we are going to look at half
reactions when we are doing the redox reactions. An acid
half reaction, we are having acid one which gives us
hydrogen ion plus the conjugate base one. Another half
reaction is acid-base two which gives us hydrogen ion
200
plus conjugate acid two. So when we write from these
two half reactions we have to write the net reaction. The
overall reaction. When you write the net reaction you’ll
add what appears in your reactants together then add
again what appears in your product. Is it clear?
Class: Yes.
Mrs Khumalo: Remember we are having two arrows in-between the
reactants and the product. So from half reaction number
one we are having acid one as your reactant. Half
reaction numbers two you are having base two as your
reactant. You are going to add acid one plus base two.
That will give you conjugate base one plus conjugate acid
two. So we are having the, the, the example that we are
having here is the reaction whereby you are having the
acid one as hydrochloric acid, the base two as ammonia
which gives us the acid two which is ammonium ion and
the base two which is the chlorine ion. So the hydrogen
here moves from hydrochloric acid and combines with the
ammonia to form the ammonium. Can you see that in
your equations?
Class: Yes.
Mrs Khumalo: And if you have to reverse the reaction, here the
ammonium will give the chlorine the hydrogen so that we
can get them hydr-, hydrogen chloride. Is it clear?
Class: Yes.
Mrs Khumalo: Remember, always an acid donates a proton and a base
must always accept a proton. Is it clear?
Class: Yes.
Mrs Khumalo: So, this is what is happening in this reaction.
[Pages over notes]
Mrs Khumalo: Okay, let’s explain the process in this equation. In the
forward reaction hydrochloric acid is the acid that donates
a proton and changes to chlorine ion and hydrochloric
acid donates a proton to the base ammonia. That
201
changes to ammonium. So, pair one, hydrochloric acid is
the acid with conjugate base chlorine ion and in the
reverse reaction ammonium is the, is the acid that
donates a proton and changes to ammonia. You, you,
you can see that in, in your equations? Can you see that?
Class: Yes.
Mrs Khumalo: The ammonium donates a proton. So the ammonia will
have to be formed because once it donates the proton we
are having them, we are having the chlorine. It donates
that proton to the chlorine so that we can have the
reverse reaction which is hydrochloric acid and ammonia.
Okay, ammonia donates a proton to the chlor-, to the
base chlorine that changes to hydrochloric acids. That is
pair number two. Ammonium is the acid with conjugate
base ammonium. Okay, the acid we are having
hydrochloric acid and ammonium. Bases, ammonia and
the chlorine. I-, is it clear so far?
Class: Yes.
Mrs Khumalo: Do, do you have any questions?
[Silence]
Mrs Khumalo: Or something that you don’t understand here?
[Silence]
Mrs Khumalo: Hmm, please don’t sleep. I know that you are from lunch.
Okay, the acid-base reaction. The acid-base reaction,
let’s look at the microscopic approach of the acid-base
reaction. When we talk about the microscopic approach
what do we mean? Who can explain it to me?
[Silence]
Mrs Khumalo: Remember if you want to say something don’t just shout,
you just raise up your hand.
[Silence]
Mrs Khumalo: Thobile?
Thobile: Something that you cannot see with your eyes.
202
Mrs Khumalo: Something that you cannot see with your naked eyes.
Okay, we saw that acid-base reaction takes place when
protons are transferred. Let’s take a look at what happens
when an acid and a base react at microscopic level. Look
at the reaction between sulphuric acid and sodium
hydroxide. Sulphuric acid we know, all know that it’s an
acid as the name says and sodium hydroxide is a base.
During titration that forms sodium sulphate or salt and
water. So, before I can continue, do you know the word
titration?
Class: No.
Mrs Khumalo: What does it mean? If you are titrating an acid and a
base what are we doing to maybe to the acid or to the
base?
[Silence]
Mrs Khumalo: What are we doing? Siphiwe? Are you with us?
Siphiwe: Yes.
Mrs Khumalo: What do we mean by titration?
[Silence]
Mrs Khumalo: What do we mean by titration [Inaudible]?
Learner: I think it’s a mixture.
Mrs Khumalo: It’s a?
Learner: A mixture.
Mrs Khumalo: Reaction? Okay, when, when, when we are mixing the
acid and the base, what are we doing?
[Child screams outside classroom]
[Silence]
Mrs Khumalo: Tsheseko? Want to say something?
Tsheseko: No ma’am.
Mrs Khumalo: Okay, let’s say, let me put a real example. Let’s say right
now I said to you I’m, I’m having a heartburn. How can
you help me?
[Silence]
Mrs Khumalo: What causes the heartburn?
203
Class: The acids ma’am.
Mrs Khumalo: The acid.
Class: Yes.
Mrs Khumalo: So, so that I can get well, what must I do?
[Silence]
Learner: You must neutralise the acids with a base.
Mrs Khumalo: I must neutralise the acid with a base. So what does the
word titration mean?
Class: To neutralise?
Mrs Khumalo: Okay, let’s continue. Let’s look at the equation here.
Sulphuric acid plus sodium hydroxide which gives us
sodium sulphate plus water. Sodium sulphate here is the
salt. Always when you are adding an acid to the base you
are neutralising. Is it clear?
Class: Yes.
Mrs Khumalo: You are neutralising that base or that acid. Is it clear?
Class: Yes.
Mrs Khumalo: So, the equation it’s known as the molecular equation
because the reactants and products are represented,
represented by means of a molecular formula. To better
illustrate what happened the ionic equation can be
written. You cannot see the ions when you are adding an
acid and a base. Is it clear?
Class: Yes.
Mrs Khumalo: When you are reacting an acid we said with your naked
eyes you cannot see the ions. You’ll just see the water
mixing together. For example here, if let’s say I didn’t put
the labels here you’ll say these two things are water. Do
you understand?
Class: Yes.
Mrs Khumalo: Yet they are not. The other one is an acid and the other
one it’s a base. So in ionic equations the sulphuric acid
will form the ions, the sodium hydroxide will form the ions.
[Phone rings]
204
Mrs Khumalo: Sorry. Switch it off.
[Hands phone to learner]
Mrs Khumalo: Okay. The sodium hydroxide also will form the ions. Then
in the product it will be some ions. Looking at this
equation you can see that there are some of the things
that do not appear on, on both sides. Is it clear?
Class: Yes.
Mrs Khumalo: They, they do appear on both sides. So when we write
the net equation we are going to leave them out because
they, they are like spectators. Do you understand?
Class: Yes.
Mrs Khumalo: We are looking at the two clubs playing. You don’t favour
any of them. You are like a spectator. Anyone wins its
fine with you. Is it clear?
Class: Yes.
Mrs Khumalo: Okay, so we will be having the hydrogen ions, the
sulphate ions and the sodium ions and the hydroxide
ions. Which gives us the sodium ions, sulphate ions and
also water. Water it’s in a liquid form. So we cannot see
the ions with your naked eyes. So that, that is why they
said it’s a reaction in a microscopic level. The bond has
broken. The bond in sulphuric acid and sodium hydroxide
before there will be any formation of new bonds, the bond
first must be broken. Is it clear?
Class: Yes.
Mrs Khumalo: Once they broke they are having the ions. The negative
ion will be attracted to the positive ion in the other
substance and the positive ion will be attracted to the
negative ion. For example here, looking at this equation,
we are having the positive hydrogen ion which has been
attracted to the negative hydroxide ion. To form what?
Class: Water.
Mrs Khumalo: Water. To form water. Then the sulphate ions are
attracted to the sodium ions. Negative and positive to
205
form the sodium sulphate. So the strong acids and bases
and their salt and water are strong electrolytes.
Electrolytes, we will learn more about electrolytes when
we are doing electro chemistry in grade twelve. This
means that they exist as ionic solution and that the ions
can act as a charge carrier which can conduct electrical
current. Water exists as a molecule. The sulphate ions
and sodium ions on both sides of the equation did not
change. So by omitting them the equation can be written
as H+ + OH- = HO. As I’ve said before that the sulphate
ions and the sodium ions are like spectators. They are
spectator ions. Is it clear?
Class: Yes.
Mrs Khumalo: So when you write the equation you write it as it is written
here. Okay, the only change in microscopic is that the
hydrogen ion of the acid and the hydroxide ion atom of
the base react with each other. In this reaction a proton
was transferred from the acid to the base to form water.
You can see the last equation.
[Silence]
Mrs Khumalo: Okay, the word that I was asking you, titration. Titration,
we are going to do titration here [Inaudible].
[DVD cuts to new scene]
Mrs Khumalo: Okay, titration. Sometimes it is important and necessary
to determine the concentration of a solution such as
hydrochloric acid. This can be done by titration. Here we
are having the chemicals here. The first one it’s sodium
hydroxide.
[Holds up sodium hydroxide]
Mrs Khumalo: And this sodium hydroxide has its concentration which is ,
mol.
[Puts down sodium hydroxide and holds up next chemical]
206
Mrs Khumalo: And we are having the acid. This acid is hydrochloric acid
but we don’t know the concentration. So, we are going to
determine the concentration.
[DVD loses sound, nothing can be heard]
Mrs Khumalo: …and some droplets. The question that I ask is what is
the standard solution? Who can tell me what is the
standard solution?
[Silence]
Mrs Khumalo: Sipho?
Sipho: The solution in which the exact concentration is known.
Mrs Khumalo: Yes, that’s correct. It’s a solution with a known
concentration. Like this one. Between the two, which one
is a standard solution?
Class: Sodium hydroxide.
Mrs Khumalo: It’s the sodium hydroxide because we know the
concentration of sodium hydroxide. Okay, you will add
two to three drops of the indicator. The indicator is
bromethymol blue. Fill the pipette to the point where
above the mark with the sulphuric acid. In this case we
are using the hydrochloric acid solution of unknown
concentration. Holding it over a basin. You will fill it and
holding it over a basin. This is your pipette. Is it clear?
Class: Yes.
Mrs Khumalo: So you hold it so that you fill everything over this basin
and so that you put it here so that the acid that you are
putting in here will not spill into your hands or whatever
you are having. Is it clear?
Class: Yes.
Mrs Khumalo: Remember acids are corrosive. They can eat away your
flesh. Okay, series of steps, okay, these steps you are
going to use when you are doing titration. You can read
all these steps and doing calculations then. With
[Inaudible] in acid-base reaction. You will have to do
calculations so that you understand how do you
207
determine the concentration of the acid. This is just an
example. We are going to do this when we are doing the
activity, the first activity on page eight. The activity on
titration. So to calculate your concentration of the acid we
use the titration. Firstly you have to balance your
equation. Why must we balance the equation?
[Silence]
Mrs Khumalo: Why is it important to balance the equation before doing
any calculations?
[Silence]
Mrs Khumalo: Banela? Why is it important to balance the equation?
Banela: To be able to know that it’s an acid or a base.
Mrs Khumalo: No. John?
[Silence]
Mrs Khumalo: Remember we have to balance the equation before doing
any calculations. Why must we balance the equation?
[Silence]
Mrs Khumalo: Arum, why must we balance the equation?
Arum: I think to give everything [Inaudible]
Mrs Khumalo: I can’t hear you.
Arum: To keep the formula constant.
Mrs Khumalo: No.
Learner: I think we have to balance the equation so that we can
know the number of mol’s we are supposed to get.
Mrs Khumalo: Yes. The number of molls it’s important in this calculation.
So you have to balance the equation. Looking at the
number of molls here, we are having one sulphuric acid,
two molls of sodium hydroxide after the equation has
been balanced. The step two you write down the given
information including the unknown. What you have to
calculate. So when, after you have written down
everything you will be able to pick up the correct formula
that we have to use in calculations. So step number three
is where you pick up the formula then you play with your
208
equation, mark what is unknown, the subject of the
formula. Then you do your substitution. Is it clear?
Class: Yes.
Mrs Khumalo: Make sure that before you do any substitution the units
are correct. You are using the correct units. Then you
substitute, you do a calculation and you write your
answer with the units again. Is it clear?
Class: Yes.
Mrs Khumalo: okay, now you are going to do this practical activity. You
are going to do practical activity to determine the
concentration of the acid. You are going to do it. I’m going
to guide you. Is it clear?
Class: Yes.
Mrs Khumalo: Okay, I, I, I think five learners will make it. They will come
in front here. They will have to come in front here and do
this four elements. Sesekho, come in front and you have
to follow the instruction. I’ve given everything to you.
What you have to do, read, understand and follow the
instructions. Okay, can you come in front?
[Learners move to the front of the classroom]
[Learners perform the experiment while speaking inaudibly to each other]
Mrs Khumalo: Yes that is a [Inaudible] flask.
[Learners continue with the experiment while Mrs Khumalo observes them
closely]
Learner: Two to three. One … two … three.
Learner: is this the pipette?
Mrs Khumalo: This is the pipette yes.
Learner: Okay we have to fill the pipette now [Inaudible]
Mrs Khumalo: This is the thing for the sulphuric acid. It’s the acid. Yes.
[Learners continue with the experiment]
Mrs Khumalo: There are some steps of what must be done during the
titration.
[Learners read through the steps]
Learner: [Inaudible]
209
Mrs Khumalo: Yes.
[Learners continue with experiment]
Mrs Khumalo: Remember acid is corrosive. Don’t let it spill over you.
[Learners move to basin and continue with experiment]
Learner: [Asks question in an African language]
Mrs Khumalo: Ke-right, yes.
[Learners continue with experiment]
Learner: [Asks question in an African language]
Mrs Khumalo: No, remember there is a, a base in that container.
[Learners continue with experiment]
Mrs Khumalo: Is it close to down there?
Learner: Yes it is.
[Learners continue with experiment]
Mrs Khumalo: Are you getting the amount of the acid? The amount of
mol you are using?
[Learners continue with experiment]
Mrs Khumalo: Sipho?
[Learners continue with experiment]
Mrs Khumalo: Sipho, add.
[Learners continue with experiment]
Mrs Khumalo: This is not properly closed.
[Closes pipette properly]
[Learners continue with experiment]
Mrs Khumalo: It is how many millilitres?
[Learners continue with experiment]
Mrs Khumalo: Do step number five.
[Learners continue with experiment]
Mrs Khumalo: What is number five? What must you do?
[Learners continue with experiment]
Mrs Khumalo: This is the [Inaudible] stand.
[Learners continue with experiment]
Mrs Khumalo: Sipho, where is step number five?
[Learners continue with experiment]
Mrs Khumalo: Where is the holder for the pipette?
210
[Moves holder towards learners]
[Learners continue with experiment]
Mrs Khumalo: Where are you going to put the fastener?
[Learners continue with experiment]
Mrs Khumalo: You have to put the pipette fast first. You are titrating
here.
[Learners continue with experiment]
Mrs Khumalo: What does number six say?
[Learners continue with experiment]
Mrs Khumalo: What is the volume first? You know the volume? Of the
acid? Okay, you write it down.
[Learners continue with experiment]
Mrs Khumalo: Okay, start titrating.
[Learners continue with experiment]
Mrs Khumalo: And open it slowly. It must come drop by drop. At the
same time you shake your solution.
[Learners continue with experiment]
Learner: What must we do?
Learner: Shake it.
Learner: Shake it.
[Learners continue with experiment]
Mrs Khumalo: And you stop when it starts changing the colour.
[Learners continue with experiment]
Mrs Khumalo: When it starts to change you stop.
[Learners continue with experiment]
Mrs Khumalo: any change?
[Learners continue with experiment]
Mrs Khumalo: It is changing.
[Learners continue with experiment]
Mrs Khumalo: Before you open it you have to check it. Mind your hands.
[Learners continue with experiment]
Mrs Khumalo: Sipho your hands! Take the tissue.
[Sipho wipes his hands with tissue]
[Learners continue with experiment]
211
Mrs Khumalo: Add the volume to the [Inaudible]. This volume to that
volume.
[Learners continue with experiment]
Mrs Khumalo: its ,?
Learner: Yes ma’am.
Mrs Khumalo: Good.
[Learners continue with experiment]
Learner: What are you talking about?
Mrs Khumalo: Okay, start titrating.
[Learners continue with experiment]
Mrs Khumalo: Start titrating.
[Learners continue with experiment]
[Learners complete experiment and return to their seats]
Mrs Khumalo: Okay class, our experiment didn’t go well. Here, when
you titrate you have seen that putting the bit of acid they
put the few drop, three drops of bromephynol blue and
the solution turned to be blue in colour. Which tells us
that it’s a base. So when they are doing the titration the
colour here must change to be yellow then they will stop
titrating. So it didn’t happen. I don’t know what’s wrong
with the acid. I did it yesterday and it worked well. So on
page eight there are some instructions that you, that you
are supposed to follow when doing titration. And when
you will, when, when you do this titration, whatever you
are doing, you have to record it. There is a table here.
The first thing, the volume of the sodium hydroxide. The
volume that you used here when titrating and the
concentration of sodium hydroxide. We all know this. It’s
given to us, nê? That when you come to the volume of an
acid, you are going to find the volume of an acid, you put
the acid here. The acid that will be able to change the
colour of this sodium hydroxide to be yellow. It’s the
volume of the acid. First, you put the volume of the acid,
the amount of acid here, you record that initial amount.
212
After the colour has changed here you will, you look for
the difference between the first volume of the acid and
the last volume of acid after titration. You write your, you
first report the volume of the acid at initial before titrating,
you write the volume that is left after titration. Then at the
end you write the difference between the two. That is the
volume that we need when we do our calculations to
calculate the concentration of the acid. Then after filling
this table here you have to answer the questions below.
The question number one, write down the balanced
equation of the reaction that took place between the
sulphuric acid and sodium hydroxide. In this case it would
be the hydrochloric acid and sodium hydroxide. You have
to fill the spaces in, in, in, in your worksheet. Write it
down. I will move around and check. Number, question
number two, you have to calculate the concentration. So
because our experiment didn’t go well we won’t calculate
the concentration. We will go straight to question number
three whereby you write down the possible hypothesis of
this investigation and you give the independent and
dependent variable for this investigation. Let’s do this. I’m
giving you only five minutes to do it.
[Learners start writing]
Mrs Khumalo: HSO write HCl. We are reacting the hydrochloric acid
with the sodium hydroxide, nê?
Class: Yes.
Mrs Khumalo: the other ones we are leaving on the table. So I want the
hydrochloric acid not the sulphuric acid.
[Learners continue with worksheets while Mrs Khumalo moves through the
class]
Mrs Khumalo: You must make sure that the equation is balanced.
[Learners continue with worksheets while Mrs Khumalo moves through the
class]
Mrs Khumalo: Finish the job.
213
[Learners continue with worksheets while Mrs Khumalo moves through the
class]
Mrs Khumalo: How about the answer for question one Siphiwe?
[Silence]
[Siphiwe moves to the blackboard to write down the answer]
Mrs Khumalo: What is the, what is the [Inaudible]?
[Siphiwe writes his answer down]
Mrs Khumalo: Siphiwe, I said instead of sulphuric acid let’s use
hydrochloric acid.
Siphiwe: Oh.
[Siphiwe erases his answer and begins again]
Mrs Khumalo: [Inaudible] what is this?
[Siphiwe continues to write]
Mrs Khumalo: Ngyeko, what is this here? What are you writing?
[Silence]
Mrs Khumalo: Siphiwe, sit down. Help him Sipho.
[Siphiwe sits down and Sipho moves to the blackboard]
Mrs Khumalo: Is he correct?
Class: Yes.
Mrs Khumalo: Is the equation balanced?
Class: Yes.
Learner: No.
Mrs Khumalo: No. who said no?
[Silence]
Mrs Khumalo: He is correct and the equation is balanced.
Class: Yes.
Mrs Khumalo: Correct.
Class: Yes.
Mrs Khumalo: Before the new bonds can be formed they need to be
broken first. Is it clear?
Class: Yes.
Mrs Khumalo: So here there will be a breakage of bonds. Remember
that what I said is by using the periodic table you can
understand which one must bond with another. Looking
214
at hydrogen in the periodic table, it’s in group one. So it
has a positive one and the chlorine it’s in group seven. It
has a negative one ion. Then the sodium here it’s having
a positive one and the hydroxide it’s having a negative
one. These two, because the charges are not the same,
they are attracted to each other but when you break your
bond here, this hydrogen carrying a positive charge will
come and bond with the ion which is negative. Is it clear?
Class: Yes.
Mrs Khumalo: The hydrogen cannot go to, to, to sodium because they
are having the same charges. Instead the hydrogen will
come and bond with the hydroxide. To form what?
Class: Water.
Mrs Khumalo: Water.
Class: Yes.
Mrs Khumalo: Is it clear?
Class: Yes.
Mrs Khumalo: To form water. Then the chlorine with its negative ion will
come and bond with the sodium to form sodium chloride.
That is how I taught you that if you want to know your
product, break the bonds first here. Put the ions by using
your periodic table you’ll be able to know which one must
bond which one on the other side. Is that clear?
Class: Yes.
Mrs Khumalo: Any question?
[Silence]
Mrs Khumalo: Okay, number two, what is the hypothesis?
[Silence]
Mrs Khumalo: Siswe, what is your hypothesis?
[Silence]
Mrs Khumalo: [Inaudible] what is your hypothesis?
[Silence]
Mrs Khumalo: What did you write?
[Silence]
215
Mrs Khumalo: Sinaswa, what did you write?
[Silence]
Mrs Khumalo: Read what you wrote.
[Silence]
Mrs Khumalo: Hmm?
[Silence]
Mrs Khumalo: [Inaudible] what is your hypothesis?
[Silence]
Mrs Khumalo: You don’t have a hypothesis? [Inaudible] What did you
write?
Learner: I said the differences between the concentrations of the
two acids will when they are, when they are combined
[Inaudible]
Mrs Khumalo: What is it? Here we are titrating. You are asked to find
the concentration of an acid. We have the acid with
unknown concentration. So your hypothesis must link
with your statement.
[Silence]
Mrs Khumalo: Asking yourself that question you’ll be able to say the
hypothesis. Remember the hypothesis is when you
answer the question.
[Silence]
Mrs Khumalo: [Inaudible] What is your hypothesis?
[Silence]
Mrs Khumalo: Prince, what did you write?
Prince: Ma’am I said when we add these acids [Inaudible].
Mrs Khumalo: Thabo?
Thabo: Uhh, when hydro- when hydrochloric acid be added to the
sodium hydroxide the reaction becomes constant.
Mrs Khumalo: Themba, what did you write?
[Silence]
Mrs Khumalo: Thando, what did you write?
[Silence]
216
Mrs Khumalo: Did you write something or are you afraid to read what
you wrote?
Learner: [Inaudible]
Mrs Khumalo: You will have to write the hypothesis for me.
[Silence]
Mrs Khumalo: You will have to fill out this worksheet. You bring it to me.
I will check because I know that some of us have written
the correct hypothesis but they are afraid of others here.
[Silence]
Mrs Khumalo: Okay, give me the variables. What is the independent
variable and the dependent variable in this investigation?
[Silence]
Mrs Khumalo: Give me the variables.
[Silence]
Mrs Khumalo: Kgotatso? What is the dependent variable?
[Silence]
Mrs Khumalo: [Inaudible]
Learner: it’s the base ma’am.
Mrs Khumalo: The base? What base?
[Silence]
Mrs Khumalo: What base?
[Silence]
Mrs Khumalo: Samantha, tell me what base?
Samantha: the independent variable is the sodium hydroxide.
Mrs Khumalo: The independent variable is sodium hydroxide. What is
the dependent variable?
Samantha: Hydrochloric acid.
Mrs Khumalo: Its hydrochloric acid.
[Silence]
Mrs Khumalo: When we were adding the acid here and opening this to
titrate it, we were looking at the volume of this acid. So
your dependent variable would be the volume that is
titrated of the acid. Okay, do you have any questions?
[Silence]
217
Mrs Khumalo: In this investigation?
[Silence]
Mrs Khumalo: Do you have any questions?
Learner: The sodium hydroxide the independent variable or the
volume of the sodium hydroxide the independent
variable?
Mrs Khumalo: Sodium hydroxide is an independent variable.
[Silence]
Mrs Khumalo: Any question on everything that we have done so far?
Mrs Khumalo: Okay, oh, Prince.
Prince: [Inaudible] is described as [Inaudible] sometimes it
[Inaudible].
Mrs Khumalo: Hmm.
Prince: And this is how [Inaudible] so [Inaudible].
Mrs Khumalo: You are on which page?
Prince: Page .
Mrs Khumalo: Okay, the, the, the segment on top? Sometimes it is
important and necessary to determine the concentration
of an acid such as hydrochloric acid. So what is the
question you have?
Prince: How can you describe [Inaudible]
Mrs Khumalo: How can you?
Prince: Describe.
Mrs Khumalo: Describe.
Prince: sometimes it is [Inaudible] it is not explaining. It is
[Inaudible].
Mrs Khumalo: Yes.
Prince: If it is not successful…
Mrs Khumalo: Sometimes it is important because you are not always
given the concentration of the acid.
Prince: So what do we do?
Mrs Khumalo: To calculate the concentration of the acid it’s when you
are not given it. You understand?
Prince: No.
218
Mrs Khumalo: You will be given everything. The concentration of, of
sodium hydroxide, of the base, but if there is no
concentration of an acid, before you can do any
calculations you have to determine it.
Learner: [Inaudible]
Mrs Khumalo: Hmm?
Learner: What is the calculation for concentration?
Mrs Khumalo: I, I don’t know, it reflects that you want the division for
titration. What is titration? I’ve asked you that question.
You didn’t answer me. Someone say.
Learner: It is an experiment.
Mrs Khumalo: It’s an experiment?
Learner: No ma’am.
Mrs Khumalo: What is titration? Who Xolilise. No. What is titration?
Learner: It’s when [Inaudible] a base.
Mrs Khumalo: It’s a base?
Class: No [Inaudible]
Mrs Khumalo: If, if you are neutralising…
Class: An acid.
Mrs Khumalo: Did we do titration here?
Class: Yes.
Mrs Khumalo: So what is it that we exactly?
Class: [Inaudible]
Learner: It’s when we test a solution for concentration.
Mrs Khumalo: Tell them.
Learner: Okay.
Mrs Khumalo: Listen. Someone is talking to you.
Learner: If you want the concentration of a solution you are going
to titrate. They both take [Inaudible] base titration.
Mrs Khumalo: What should be the term?
[Silence]
Mrs Khumalo: The process during the acid-base reaction. What will you
say? I thought that, that question was in your questions,
nê?
219
Class: Yes.
Mrs Khumalo: When you are writing during the exam. What would you
say?
[Silence]
Mrs Khumalo: When you are adding an acid to a base, what are you
doing?
Learner: Titrating.
[Mrs Khumalo shakes head no]
Mrs Khumalo: You are neutralising.
[Silence]
Mrs Khumalo: Okay, any questions so far before we continue?
[Inaudible]
Learner: On page [Inaudible] during the base reaction. My
question is, is a base capable of donating a proton?
Mrs Khumalo: a base?
Learner: Is a base..
Mrs Khumalo: A base?
Learner: Yes.
Mrs Khumalo: No. a base always accepts the proton.
[Silence]
Mrs Khumalo: Are you happy?
Learner: Yes ma’am.
Mrs Khumalo: Okay let’s continue, our time is running out.
[Silence]
Mrs Khumalo: Okay, let’s do the last part of our lesson. The redox
reaction.
[Silence]
Mrs Khumalo: In the redox reaction you give special names to the two
substances which exchange electrons. That is on, on
page nine. The top of page nine. The substance which is
atom- io- [Inaudible] and donates an electron is called a
reducing agent. You, you must know those terms. They
are very, very important. A reducing agent undergoes a
process of oxidation and is oxidised by a substance that
220
causes the oxidation, which is called the oxidising agent.
So the reducing agent reduces the substance and, which
is oxidising agent to which it gives electrons. So this term
switcher are important, very important. Know and
understand that because you are going to use them again
next year. Remember we are, we are now building the
walls of our house [Inaudible]?
Class: Yes.
Mrs Khumalo: You can tell we start with the foundation, walls, you build
the roof next year. Okay, a substance with atoms, ions or
molecules that gain electron is called the oxidising agent.
An oxidising agent undergoes the process of reduced-,
reduction because it is reduced by the substance that
cause the reduction which is called the reducing agent.
The oxidising agent oxidises the substance which is the
reducing agent to which it receives electrons. From the
oxidation and reduction half reaction above we can
deduce the following about the reaction between
magnesium and oxygen. The reaction between
magnesium and oxygen for magnesium, magnesium is a
reducing agent because it is the substance that donates
electrons. Where do you get magnesium in your periodic
table?
Class: Group two.
Mrs Khumalo: magnesium undergoes the process of oxidation because
it is oxidised by the oxidising agent, oxygen gas that
caused the oxidation. Magnesium as the reducing agent
is, reduces oxygen which is the oxidising agent. For
oxygen, oxygen is the oxidising agent because it is the
substance that gains electrons. Oxygen undergoes the
process of reduction because it is reduced by the
reducing agent. The magnesium that causes the
reduction, the magnesium is a reducing agent in oxygen.
Oxygen as an oxidising agent oxidises magnesium which
221
is a reducing agent. Okay, because redox reactions
cause electron transfer, oxidation and reduction are not
the only reaction that takes or releases oxygen as initially
thought by scientists. There are many redox reactions
that have no oxygen in their reaction. I, I, I think we have
seen that in your books. Let’s summarise in terms of
electron transfer. Oxidation is the donation and release of
electrons by a substance and reduction is the gain or
receiving of electrons by a substance. An oxidation-
reduction reaction which is a redox reaction is a reaction
that takes place when electrons are transferred. If there is
no transfer of electrons, there is no oxidation-reduction
reaction. An oxidising agent is a substance that accept
electrons and is reduced. A reducing agent is a
substance that donates electrons and is oxidised. An
example is a reaction between silver nitrate and
hydrochloric acid, a redox reaction. Okay, for the solution
we have to follow some steps. Step number one write the
balanced chemical equation for the reaction that takes
place. You are having the silver nitrate, hydrochloric acid
and silver chloride and nitric acid. So the equation is
balanced. So the step number two, now we are going to
break each and every compound into its ions. When you
are breaking each and every compound into its ions you
are having the silver nitrate, the silver nitrate, hydrogen,
chlorine, silver chlorine and hydrogen nitrate. So looking
at these ions, which is step number three, in your
reactant you are having silver with how many ions?
Learner: One.
Learner: Two.
Mrs Khumalo: Silver, how many ions?
Class: It’s one, just one.
Mrs Khumalo: Remember I’ve said to tell that a compound is in ionic
form you must see the signs on top, nê?
222
Class: Yes.
Mrs Khumalo: The plus and minus.
Class: Yes.
Mrs Khumalo: How many ions does silver have on your reactant?
Class: It has one.
Mrs Khumalo: In your product?
Class: It has one.
Mrs Khumalo: Nitrate?
Class: It’s one as well.
Mrs Khumalo: Your product?
Class: Plus one.
Mrs Khumalo: Hydrogen?
Class: Plus one.
Mrs Khumalo: In your product?
Class: Plus one.
Mrs Khumalo: Chlorine?
Class: Minus one.
Mrs Khumalo: In your product?
Class: Minus one.
Mrs Khumalo: Is there any change in our [Inaudible]?
Class: No.
Mrs Khumalo: They are the same on both reactants and products. So,
this e-, this equation it’s a redox reaction equation?
Class: No.
Mrs Khumalo: No. there is no reducing, there is no oxidising of anything
here. Everything, product and the reactant is the same.
Okay, you decide which substance donates electrons and
which one accepts electrons. So looking at this equation,
none of them donates or accepted electron. So this is not
a redox reaction. Let’s look at the second example. In the
reaction between zinc and hydrochloric acid, is the zinc
reducing the hydrochloric acid? If so, write the oxidation
and reduction half reaction. Solution, firstly the balanced
equations are very important. Write the formulas
223
correctly. Balance your equations. I, I’ve seen some of
you were writing, maybe they were formulas from the
space, I don’t know. So please write the correct formulas.
We are having zinc plus hydrochloric acid, getting the
zinc chloride plus hydrogen gas. The step number two,
place the correct charges in the reactions. Even in the
equation here, we are having the zinc that’s plus a
hydrochloric acid. Can you see there’s a space where
there is nothing?
Class: Yes.
Mrs Khumalo: Yeah, put the plus. The zinc, hydrochloric acid then zinc
chloride and hydrogen gas. Okay, what is the charge of
zinc?
[Silence]
Mrs Khumalo: Does zinc have a charge?
Class: Yes.
Mrs Khumalo: In a solid form? Does it have a charge?
Class: Yes.
Mrs Khumalo: No. then we are having hydrochloric acid which we are
having the hydrogen and the chlorine. They both have
charges. Then on the other side we have the zinc
chloride now. The zinc it is having now a charge and the
chlorine is having its own charge. Lastly we are having
the hydrogen. The hydrogen is having no charge.
Class: Yes.
Mrs Khumalo: Okay, looking at each separate, the zinc started with no
charge. Can you see that?
Class: Yes.
Mrs Khumalo: In your reactant and ended up with?
Class: A charge.
Mrs Khumalo: Positive two.
Class: Positive two.
Mrs Khumalo: Is it an increase or a decrease?
Class: Increase.
224
Mrs Khumalo: Okay, let’s go to the second one is the hydrogen.
Hydrogen started with?
Class: A charge.
Mrs Khumalo: Plus one.
Class: Yes.
Mrs Khumalo: And ends up with?
Class: No charge.
Mrs Khumalo: No charge. Is it an increase or a decrease?
Class: Decrease.
Mrs Khumalo: Then the last one is chlorine. Chlorine started with?
Class: No charge.
Mrs Khumalo: Negative one and ended up with?
Class: Negative one.
Mrs Khumalo: Is there any difference there? Decrease or increase?
Class: No.
Mrs Khumalo: Nothing is happening.
Class: Yes.
Mrs Khumalo: Okay, then let’s go to step number four. Decide which
substance donates an electron and which one accepts an
electron. Looking at this, zinc donates an electron. Zinc is
oxidised and is therefore a reducing agent. Hydrogen
accepts an electron. Hydrogen is reduced and therefore
is an oxidising agent. Therefore the reaction is redox
reaction. Because there is an exchange of electrons. Can
you see that?
Class: Yes.
Mrs Khumalo: Unlike the first example. Nothing happened in the first
example. Okay, the oxidation half reaction, writing the
zinc gives us the zinc plus two electrons. Zinc with, in
ionic form it’s, sorry, plus two electrons. The reduction
half reaction, writing the hydrogen in an ionic form plus
electrons giving us hydrogen. This hy-, half reactions, you
will always be provided by the standard electron table.
225
When you are writing a test or exam you will be provided
with that and you have to write them correctly.
[Silence]
Mrs Khumalo: Okay, before we can go to the next page, is it clear of the
redox reactions?
Class: Yes.
Mrs Khumalo: Do you have any questions? Do you understand what’s a
redox reaction? What is happening there in redox
reactions?
[Silence]
Mrs Khumalo: Okay, let’s look at the last part of our lesson. The
oxidation states and oxidation numbers. For us to assign
the oxidation numbers you must know the rules. The
rules are written here. It’s rule number one up to rule
number nine.
Class: Yes.
Mrs Khumalo: You will give yourself time and read and understand
these rules. Is it clear?
Class: Yes.
Mrs Khumalo: I won’t go through them now. Read and understand the
rules and I know that you know the rules but at times you
forget when you are writing an activity or a test. Please
know these rules. Read them and understand them. Don’t
just read them, understand them. Okay, let’s look at this
in the box. Oxidation is the increase in oxidation number
of an element during a reaction. An increase in the
oxidation number of an element during a reaction will
indicate which element was oxidised. Reduction is a
decrease in oxidation number of an element during
reaction. A decrease in the oxidation number of an
element during the reaction indicates which element was
reduced. You must understand the oxidation and
reduction in terms of oxidation numbers. Okay,
recognition of oxidati-, oxidising and reducing agents.
226
Oxidation numbers can be used to recognise the oxidisg
and reducing agent that are involved in a redox reaction.
The following steps indicate the method to be followed.
[Inaudible] oxygen, we know that oxygen appears in
group six in the periodic table. So oxygen has a balance
of negative two. So which, when oxygen is having
negative two, for the element to be neutral, for copper
oxide to be neutral, copper must have plus two. So
oxygen is having negative two, copper its plus two. Going
to the second one. Copper or nitrogen ammonium, sorry.
Hydrogen it’s in group one. It has plus one and ammonia
it’s in group, like I taught you it’s in group five. It has a
negative five. From the rule number, number one, the
copper and nitrogen gas are not bonded with any element
so they are having the oxidation numbers of zero. Then
when we go to water, hydrogen it’s having plus one,
oxygen it’s having negative two on both sides of the
equation. Can you see that?
Class: Yes.
Mrs Khumalo: The copper it’s having plus two and negative and zero
ions sorry, so the copper, what is happening to the
copper? It started with plus two then zero. What is
happening?
Class: It’s reducing.
Mrs Khumalo: it’s decreasing. Then the next one. The next one it’s the
nitrogen. Nitrogen started with negative three. These
lines have changed a little bit. Can you see that?
Class: Yes.
Mrs Khumalo: so the line is pointing at nitrogen. Nitrogen and the
copper. So looking at nitrogen, nitrogen started with
negative three and ended up with zero. Is it increasing or
decreasing?
Class: increasing.
227
Mrs Khumalo: Increasing. So by assigning each and every element in
your equation, assigning the oxidation numbers, you will
be able to tell which one is the oxidation and which one is
the reduction. So the oxidation number of copper
decreases from two to zero and therefore copper oxide is
reduced to copper. Copper oxide therefore is the
oxidising agent. The oxidation number of nitrogen
increases from negative three in ammonium to zero in
nitrogen. Ammonia is oxidised to nitrogen therefore
ammonia is the reducing agent. You can see the number
from negative three to zero. The numbers are increasing.
Is it clear?
Class: Yes.
Mrs Khumalo: Okay, did you have any questions?
Class: No.
Mrs Khumalo: Okay, the activity on page thirteen, go and do it at home
as homework. We will do corrections during our period
tomorrow.
Class: Yes.
Mrs Khumalo: do it as the homework.
Class: Yes.
Mrs Khumalo: Alright, thank you very much.
Class: You’re welcome.
[End of recording]
228
G.2: Class Observation - Mr Mashigo Researcher: This is the lesson observation recording of Mr Mashigo’s
class.
Mr Mashigo: Morning.
Class: Morning sir.
Mr Mashigo: Now, today we are going to focus on acids and bases but
our practical investigation will then be on how acids
reacts with bases. But the first thing that I’d like to find out
from you, do you know what acids are?
Class: Yes.
Mr Mashigo: Okay, those who know give me an example of one acid
that you know.
Learner: An acid is something that you use and can release a
proton.
Mr Mashigo: She’s saying that an acid is a substance that can release
a proton. .
Learner: Acid can be used in a product where that acid have that
charges.
Mr Mashigo: Then some of them the household things that we make
use of acids are that. Yes.
Learner: An acid has a ph scale of lower than seven.
Mr Mashigo: Lower than seven. Now, metals react with oxygen and
non-metals react with oxygen. Now, the oxides of metals
like for instance now, look at this. Take for instance
magnesium reacting with oxygen and then we end up
with magnesium oxide. Now, the oxides of metals when
dissolved in water they produce alkali substances. Now,
the oxides of non-metals like for instance now let’s take
carbon, it’s a non-metal reacting with oxygen. Then we
end up with carbon dioxide. Now, this couple that oxides
because it’s an oxide of a non-metal, when dissolved in
water the solution becomes acidic. Remember oxides of
metals when they dissolve in water it’s all, , alkali
229
solutions but the oxides of non-metals when dissolved in
water they form acidic solutions. Now, an acid some of
the properties of an acid that I think you are aware of is
that now an acid can change a blue litmus paper to which
colour?
Class: Pink.
Mr Mashigo: To red. Is that it?
Class: Yes.
Mr Mashigo: And then a base can change a blue, a, a red litmus paper
to?
Class: Blue.
Mr Mashigo: Blue.
Class: Blue.
Mr Mashigo: [Inaudible] Now, acids when they react with metal oxides,
carbonates, metals and um, metal hydrogen carbonates,
they neutralise the acidity of a solution. Let’s us start by
looking at the reaction of an acid with a metal. Not metal
oxide now but with a metal. Let’s take zinc. Zinc reacts
with hydrochloric acid and then what happens is,
remember for a reaction to occur all bonds must be
broken so that new bonds can be formed, and obviously
here what happens is the link between hydrogen and
chlorine will be broken. And I do mention that , an acid is
a substance that imparts the hydrogen protons in
solutions. Now we end up with a hydrogen proton and a
chloride ion. Now this chloride ion will then combine so
that there will be a bond formed between zinc and a
chloride ion. Then we end up with zinc chloride and
hydrogen. Now, what are this name, this simply means
that now whenever a metal reacts with an acid [Inaudible]
is formed and hydrogen will be the product. Let’s take
another , acid. Say for instance now we take ,
magnesium reacting with nitric acid. It’s a metal and an
acid like I mentioned earlier all bonds will be broken.
230
Leaves me a nitric ion and the hydrogen and then SE and
then what happens now, we end up with magnesium
nitrate plus hydrogen. So whenever an acid reacts with a
metal a solid and hydrogen is released. In other words
now whenever an-, any metal reacts with an acid then a
solid and hydrogen will be the products. But now let’s
look at the substances that um, neutralises this, the acid.
Like for instance now, look at the reaction of a metal
oxide with an acid. You remember we said a metal reacts
with oxygen and gives us a metal oxide. But this metal
oxide when dissolved in, in, a, in water they form alkali
solutions and you mentioned again that now when a non-
metal reacts with oxygen it forms a non-metal oxide and
that metal oxide when dissolved in water forms an…
Class: Acidic solution.
Mr Mashigo: …acidic solution. Now let’s take a reaction of an acid with
a metal oxide. Say for instance now we take HCL plus
magnesium oxide. Now, what is it that makes us to be, to,
to be, to see that now that is an acid. You’ll remember we
mentioned that now an acid imparts the hydrogen
protons. You get that?
Class: Yes.
Mr Mashigo: Now, what happens is all bonds will be…
Class: Broken.
Mr Mashigo: …broken. Now a bond between a chloride ion and
hydrogen proton will, will be broken hence we have
hydrogen proton and a chloride ion. And again here a
bond will be broken between magnesium and oxygen.
Then we end up with magnesium ions and the oxide ion.
Now to make this easier for you to understand when
bonds are broken whatever is positive this side will then
combine with whatever is negative that side. And then
this one negative will combine with that one and if you
can look carefully now you will find that now we end up
231
with magnesium chloride plus now can be hydrogen and
oxygen. What do you think it will form?
Class: Water.
Mr Mashigo: Water isn’t it?
Class: Yes.
Mr Mashigo: Then we end up with water and one more thing. Do we
now have the hydrogen protons in that solution? That
makes the solution to be acidic.
Class: No we don’t.
Mr Mashigo: No. meaning that now that metal oxide has destroyed the
acid. Now we end up with solid and water.
Class: Water.
Mr Mashigo: Now, let me quickly look and show you another one.
Where now it’s a carbonate and an acid. Now let’s take
um, sodium carbonate and react it with nitric acid. Again
all bonds will be broken.
Class: Broken.
Mr Mashigo: Then we have a bond like this broken and we end up with
sodium ions but two of them and a carbonate ion. And
then again all bonds are broken.
Class: Broken.
Mr Mashigo: Then we end up with the hydrogen proton and a nitrate
ion. Now, from my, my previous explanation, sodium ion
will react with which ion here?
Class: Nitric acid.
Mr Mashigo: A nitrate ion.
Class: Ion.
Mr Mashigo: You see that?
Class: Yes.
Mr Mashigo: And then we end up with sodium nitrate which is a?
Class: Solid.
Mr Mashigo: Solid. What else do you think will be the product?
Class: Hydrogen [Inaudible]
232
Mr Mashigo: No in this case now what happens is we end up with
carbon dioxide plus what?
Class: Water.
Mr Mashigo: Water. You get this?
Class: Yes.
Mr Mashigo: So you realise that now after this reaction do we have the
hydrogen protons that are on their own?
Class: No.
Mr Mashigo: In order to give the solution an acidic an acidic ,
properties?
Class: No.
Mr Mashigo: No. so in other words now, the metal oxide the
carbonates and , lastly the hydrogen carbonates also
react with acids and destroy the acid properties. By doing
what? By taking that hydrogen proton and combing in it
with oxygen to form water and then we no longer have an
acid.
Class: Acid.
Learner: So sir does that mean that if we add the acidic solution
with the metal outside we get , like our solution has to
have water in it?
Mr Mashigo: Although you will not need a solution to see that now
where this is the water from the result of hydrogen
reacting with oxygen. Like in this case now you will be
able to see that because the solution already has some
water. You have this hydrogen oxygen…
Class: Oxygen.
Mr Mashigo: …but the most important thing is what gives the acid the
acidic properties? Is the presence of hydrogen like you,
hydrogen protons that you mention.
Learner: So sir obviously in our solution there has to be HO.
Mr Mashigo: There have to be…
Learner: …combined like acidic solution with metallic oxide. Our
solution has to have um, HO?
233
Mr Mashigo: It must have a solid and water. Now let me quickly recap
here. When an acid react with an, with a metal not a
metal oxide, the products are solid and hydrogen. When
an acid reacts with a metal oxide the products are solid
and water. When an acid reacts with a carbonate like in
this case our product will be solid. Carbon dioxide and
water and then when an acid again reacts with sodium
hydrogen carbonate the products again are going to be a
solid. Let’s take some chloric acid this time then we end
up with sodium sulphate and that is a solid plus carbon
dioxide plus water. Now the reactions that I’ve made
mention of that destroys the acidic , properties, we say all
of these oxides or carbonates neutralises the acid.
Destroy the acid properties. Now I’d like us now to look at
that handout that I gave you, the worksheet.
[Silence]
Mr Mashigo: Now if you look at the worksheet you’ll realise that now
the experiment is to determine the reaction of acid on
alkalis. To determine the action of an acid on alkalis. In
other words now how the acid reacts with an alkali but let
me ask you a question. When an acid reacts with an
alkali which products do you expect?
Class: Water.
Mr Mashigo: What will be formed?
[Silence]
Mr Mashigo: Let’s hear this side. What do you say?
Learner: [Inaudible]
Mr Mashigo: When an acid reacts with a base what happens?
[Silence]
Mr Mashigo: Or let me put it basically this way, when an acid reacts
with a base what will be the products?
Learner: [Inaudible]
Mr Mashigo: .
234
Learner: The product is a harmless salt because an acid and a
base when they neutralise each other than a salt…
Mr Mashigo: So one of the products will be a salt and what else?
Class: And water.
Mr Mashigo: And water isn’t it? But when it’s a carbonate what will be
the product?
Learner: [Inaudible]
Mr Mashigo: .
Learner: A salt and a carbonate with water.
Mr Mashigo: Carbon dioxide and water. Correct?
Class: Yes.
Mr Mashigo: Right, now, here I have calcium hydroxide which is a
base. Now, to start with we can identify the bases by the
hydroxide ion. Like the book said an acid is a substance
that imparts the hydrogen protons in water. In the
nineteenth century there was a guy called Arminius. He
was saying an acid is a substance that donate hydrogen
protons in solutions and a base like for instance now, look
at this base, sodium hydroxide, calcium hydroxide and
then potassium hydroxide. What is common about them
all?
Class: They are all hydroxides.
Mr Mashigo: The hydroxide ions. So what is what that guy was saying.
When these dissolve in water you end up with the sodium
ions plus the hydroxide ions and that is a base.
Class: A base.
Mr Mashigo: You have that?
Class: Yes.
Mr Mashigo: But that changed later on when , a guy like Lowry and
Bronsted gave a different definition but we’ll, we’ll come
to that one. Alright, now this is calcium hydroxide, the one
that I have written here. And then this is potassium
hydroxide and then we have sodium hydroxide, but
unfortunately this one is already a solution. Alright?
235
Class: Yes.
Mr Mashigo: Fine. Now we have here nitric acid. This is the acid that
I’m talking about and then we have sulphuric acid.
Class: Acid.
Mr Mashigo: This is the one that , I indicated here and then we have
hydrochloric acid. Now, according to the instruction sheet
tell me what must I do? What is the first thing to do?
Class: Prepare the solution [Inaudible]
Mr Mashigo: Fine, now let’s prepare a solution of calcium hydroxide
because this one is already a solution. You get that?
Class: Yes.
Mr Mashigo: So that we can see.
[Silence]
Mr Mashigo: So this is calcium hydroxide. As you can see it looks like
powder isn’t it?
Class: Yes.
Mr Mashigo: But now look at what happens here. That it clearly
dissolves in this water.
Class: Yes.
Mr Mashigo: It does doesn’t it?
Class: Yes.
Mr Mashigo: Now let’s test and see what are the solutions. What is the
solutions? Whether the solution is acidic or basic?
Class: Yes.
Mr Mashigo: Now like we mentioned earlier that uh, a base changes
the colour of a litmus paper from…
Class: Red.
Mr Mashigo: …red to…
Class: Blue.
Mr Mashigo: …blue. Now here is the litmus paper. We have a red
litmus paper. Now, look at what happens here.
Class: It’s [Inaudible]
Mr Mashigo: You see that?
Class: Yes.
236
Mr Mashigo: So it means now this is a basic solution.
Class: Solution.
Mr Mashigo: Alright?
Class: Yes.
Mr Mashigo: But it’s calcium hydroxide.
Class: Hydroxide.
Mr Mashigo: Fine. Now, I pour a little bit of this inside.
[Pouring sound]
Mr Mashigo: And then let’s look at the blue litmus paper in an acid.
[Silence]
Mr Mashigo: Now, here is nitric acid.
Class: Nitric acid.
Mr Mashigo: Now I pour a little bit of an acid in this container.
[Silence]
Mr Mashigo: Fine. Now we said an acid changes a blue litmus paper
from blue to…
Class: Red.
Mr Mashigo: …red.
[Silence]
Mr Mashigo: Look at the colour of that litmus paper.
Class: It’s red.
Mr Mashigo: Already red.
Class: Red.
Mr Mashigo: You see that?
Class: Yes.
Mr Mashigo: Now, we have an alkali solution.
Class: Solution.
Mr Mashigo: Of calcium…
Class: Calcium hydroxide.
Mr Mashigo: …hydroxide. And we have an acid.
Class: Acid.
Mr Mashigo: Alright.
Class: Yes.
237
Mr Mashigo: Now, when we throw in a litmus paper after this have
thoroughly mixed one would not expect a litmus paper to
change from red to blue or from blue to red. Why?
Because a bond must have been formed. Because look
at what happens here. We said , a base neutralises the
acidic properties now let’s look at the reaction that we are
talking about. Please look careful. In this solution we
know that now we have calcium…
Class: Hydroxide.
Mr Mashigo: …hydroxide. So we have calcium hydroxide reacting with
what acid?
Learner: Nitric…
Mr Mashigo: Nitric?
Class: Acid.
Mr Mashigo: Acid.
[Silence]
Mr Mashigo: Now, all the bonds are…
Class: Broken.
Mr Mashigo: …broken and new bonds are…
Class: Formed.
Mr Mashigo: …formed. Then we end up with calcium ion and the two
hydroxide ions. Now here again all bonds are?
Class: Broken.
Mr Mashigo: Broken. We end up with the hydrogen…
Class: Protons.
Mr Mashigo: …protons and the nitrate…
Class: Ions.
Mr Mashigo: …ions. Now like I said earlier, what is positive?
Class: [Inaudible]
Mr Mashigo: From my bond is what is negative on the other
substance. And what reaction forms the bond? Now let
me quickly find out, what will you say when this hydrogen
proton from an acid reacting the hydroxide ion, what do
you think will be the product?
238
Learner: Hydrogen proton.
Mr Mashigo: Hydrogen proton and a hydroxide ion.
Learner: Water.
Mr Mashigo: Water, isn’t it?
Class: Yes.
Mr Mashigo: Then we must have water. And then of course now
calcium and the nitrate ion then we end up with…
Class: Calcium.
Mr Mashigo: …calcium…
Class: Nitrate.
Mr Mashigo: …nitrate. Do we, do we now have the acidic or basic
properties here?
Class: No.
Mr Mashigo: No, we can’t have. We no longer have the hydroxide ion
that characterises the base.
Class: Base.
Mr Mashigo: We no longer have the hydrogen proton that
characterises the acid.
Class: Acid.
Mr Mashigo: Isn’t it?
Class: Yes.
Mr Mashigo: Now let’s find out whether that is true or not. Now let’s
pour a little bit of, you remember it’s a, it’s an alkali base.
Class: Base.
[Silence]
Mr Mashigo: And then this is the acid.
Class: Acid.
[Silence]
Mr Mashigo: But one should do one thing, if chemically equivalent
quantities have mixed, in other words now, they are fifty-
fifty…
Class: Fifty-fifty.
Mr Mashigo: …one would expect the solution that I’m explaining here.
Class: Yes.
239
Mr Mashigo: You get that?
Class: Yes.
Mr Mashigo: But if there is a certain percentage of a base higher than
that of an acid what can be the potential to see that
colour change? [Inaudible]
Class: [Inaudible]
Mr Mashigo: Fine. Now let’s see. If we drop in this one. So one
expects that now the colour to change from this one, one
would expect the colour to change for it is an a-, the
solution is acidic. It must change from blue to?
Class: Red.
Mr Mashigo: Red. Now let’s see. If it works out.
[Silence]
Mr Mashigo: So this means now here we have more of the acid…
Class: Acid.
Mr Mashigo: …than the base…
Class: Base.
Mr Mashigo: …but let’s try to make them to be equal.
[Silence]
Mr Mashigo: See?
Class: .
Mr Mashigo: So there’s equation to [Inaudible] now when we put in this
, litmus paper. There shouldn’t be a colour change.
Class: Yes.
Mr Mashigo: You see that?
Class: Yes.
Mr Mashigo: So that it means that now there are no longer…
Class: Acidic.
Mr Mashigo: …acidic properties or…
Class: Basic.
Mr Mashigo: …basic properties. In other words now that would mean if
this doesn’t change a colour that would mean that now
we have equal concentrations of the hydroxide…
Class: Ions.
240
Mr Mashigo: …ions and the hydrogen…
Class: Protons.
Mr Mashigo: …protons.
[Silence]
Mr Mashigo: But the other important thing is you must remember that
we have strong acids and weak acids. Strong bases as
well as…
Class: Weak bases.
Mr Mashigo: …weak bases. Now, note one thing, now if the acid is
strong and the base is weak you will find that now the
solution pervades or we will find that now the acidic
properties are still there. You get that?
Class: Yes.
[Silence]
Mr Mashigo: So it means that the acid is?
Class: Strong.
Mr Mashigo: Strong. Correct?
Class: Yes.
Mr Mashigo: But the point is when an acid…
Class: Acid.
Mr Mashigo: …reacts with a…
Class: Base.
Mr Mashigo: …base the acidic properties are…
Class: Destroyed.
Mr Mashigo: …destroyed. Alright?
Class: Yes.
[Silence]
Mr Mashigo: And then I’ll give you the notes sometime in the course of
the week because they are going to type them. Alright, be
from what we have and …
[Silence]
Mr Mashigo: Just wait a minute.
[Silence]
Researcher: [Inaudible]
241
Mr Mashigo: Two-two.
Researcher: Has it happened?
Mr Mashigo: It’s happened now. There’s I can continue. Alright, now.
[Silence]
Mr Mashigo: Okay. Now, listen, the, how we started the people is not
let go. Now, remember those things that now, if I had a
pipette with me I would be able to make a so-. But now
let’s try another one. Let’s take now , a solution of
potassium hydroxide. Alright?
Class: Yes.
Mr Mashigo: And nitric acid.
Class: Nitric acid.
Mr Mashigo: Now here one expect that a
[Silence]
Mr Mashigo: Potassium hydroxide will impart the hydroxide ions in the
solution and , the acid that reacts will then be imparting
the hydrogen protons. And with the hydrogen protons and
, hydroxide ions combined obvious we will end up with
water.
Class: Water.
Mr Mashigo: And the acidic properties are destroyed. We have salt
and…
Class: Water.
Mr Mashigo: …water. Now to recap the lesson [Inaudible] One, we
said an acid reacts with a metal and hydrogen salt and
hydrogen is the product. And then we said that now an
acid reacts with a metal oxide and salt and water are the
products. Now when acid reacts with a carbonate what
will be the product?
Class: Salt and water and carbon dioxide.
Mr Mashigo: Salt, carbon dioxide and water. But there is another base
like for instance now ammonia. Ammonia it’s a base…
Class: Base.
242
Mr Mashigo: When it reacts with an acid a salt is formed but no water
is formed. Like for instance now take ammonia NH,
ammonia is mostly used to remove certain [Inaudible].
Now it combines with acid and you remember that all
bonds can be…
Class: Broken.
Mr Mashigo: …broken but now the product here, now look carefully at
this homework. Will you expect water to be formed?
Class: No.
Mr Mashigo: Why not?
Class: Because there’s no oxygen.
Mr Mashigo: Because there is no oxygen. Isn’t’ it?
Class: Yes.
Mr Mashigo: So in this case now what happens is you enter this
breaking up and then they end up with hydrogen…
Class: Protons.
Mr Mashigo: …protons and the chloride…
Class: Ions.
Mr Mashigo: …ions, then this through what we call the, the [Inaudible]
covalent bonds. Then we have amo-, ammonium…
Class: Ions.
Mr Mashigo: …ions. This is remember that now, this is ammonia, this
is ammonium ions and what we have here again we have
the chloride…
Class: Ions.
Mr Mashigo: …ion and then the two now combine and form
ammonium…
Class: Chloride.
Mr Mashigo: …chloride. Which is a..
Class: Solid.
Mr Mashigo: …solid but in this case now we don’t have…
Class: Water.
Mr Mashigo: …water. Alright?
Class: Yes.
243
Mr Mashigo: [Inaudible] Now let’s go back to this one. Let’s make a
solution of, I’ve already had a solution of sodium
hydroxide. Now…
[Silence]
Mr Mashigo: In this solution of sodium hydroxide which ions do you
expect to be there?
[Silence]
Mr Mashigo: Which ions can you expect in this?
[Silence]
Mr Mashigo: Its sodium hydroxide.
Class: [Inaudible]
Mr Mashigo: We said a, a hydroxide ions [Inaudible] because it’s a
base.
Class: Base.
Mr Mashigo: It’s sodium hydroxide, fine. Now, let’s see if we take the
same acid, nitric acid, but first of all look at this.
[Silence]
Mr Mashigo: [Inaudible]
[Silence]
Mr Mashigo: let’s take a red litmus paper and then from the red litmus
paper let’s see whether it changes colour.
[Silence]
Mr Mashigo: So one would expect a red litmus paper to change from
which colour to which colour?
Class: From red to blue.
Mr Mashigo: From red to blue.
Learner: Blue.
Learner: Blue colour.
Mr Mashigo: there it is.
Class: We see.
Mr Mashigo: You see that?
Class: Yes.
Mr Mashigo: It changes from red to blue.
Class: Blue.
244
Mr Mashigo: But let’s try to neutralise it.
[Silence]
Mr Mashigo: Okay let’s take this same, okay let’s take a strong acid…
Class: Yes.
Mr Mashigo: …like hydrochloric acid because the hy-, the bases like
sodium hydroxide, potassium hydroxide and , calcium
hydroxide are actually strong bases.
Class: Bases.
Mr Mashigo: The bases that I have that have hydroxide ions are the
strong bases.
Class: Bases.
Mr Mashigo: Now let’s take , this ni-, sulphuric acid.
Class: Acid.
Mr Mashigo: But now people when you handle this things remember
you must always have your protective clothes on.
Class: Yes.
Mr Mashigo: because I’m careful it won’t take, because acids are
corrosive. They can eat up the clothes or your skin.
Class: Yebo sir.
Mr Mashigo: But now because I am careful.
[Silence]
Mr Mashigo: Why does it turn back to red?
Class: It’s an acid.
Mr Mashigo: Hah?
Class: It’s an acid.
Mr Mashigo: The base is too strong.
Class: Yes.
[Silence]
Mr Mashigo: Now.
[Silence]
Mr Mashigo: Okay.
[Silence]
Mr Mashigo: I’ll do the [Inaudible] now. [Inaudible] I’m going to fetch.
Now that we have this things to mix that can actually tell
245
us how much of acid is in there. How many millilitres of
an acid are there and millilitres of a base that are?
Class: There.
Mr Mashigo: I think it will be appropriate now to use our, our
instrument that will measure accurate quantities. You get
that?
Class: Yes.
Mr Mashigo: Fine. Now, I think let us do a solution of, or this time let’s
make potassium hydroxide. Now as you can see, look at
how it looks like.
Class: It’s a solid.
Mr Mashigo: It’s a solid, nê?
Class: Yes.
Mr Mashigo: Looks like a solid. Alright?
Class: Yes.
Mr Mashigo: But now remember strong acids like this one are
corrosive just like acids.
Class: Acids.
Mr Mashigo: They can , destroy your tissues of the hand, of you’re, of
your skin.
[Silence]
Mr Mashigo: Now here is the solution.
Learner: Sir?
Mr Mashigo: ?
Learner: Sir do you keep this on?
Mr Mashigo: That is why I normally say do the lab you don’t leave of
[Inaudible].
Class: Yes.
[Silence]
Mr Mashigo: Fine. Now, look, look at the top, look at the table now.
Alright?
Class: Yes.
Mr Mashigo: Fine.
[Silence]
246
Mr Mashigo: Now, look at this. How many mils, millilitres?
Class: [Inaudible]
Mr Mashigo: [Inaudible] you can see.
Learner: [Inaudible]
Mr Mashigo: twenty-five millilitres. You see that?
Class: Yes.
Mr Mashigo: Fine. Now, look at the table. We have this twenty-five
millilitres.
Class: Millilitres.
[Silence]
Mr Mashigo: Of the base.
Class: Yes.
[Silence]
Mr Mashigo: And now let’s take
[Silence]
Mr Mashigo: Nitric acid.
Class: Acid.
[Silence]
Mr Mashigo: Remember I’m supposed to be having gloves on my
hands but because I’m careful.
[Laughter]
Mr Mashigo: You can see that’s why this.
[Laughter]
Mr Mashigo: Alright, now let’s see.
[Silence]
Mr Mashigo: Now it’s the acid. I gave the same quantities.
Class: Quantities.
Mr Mashigo: Correct?
Class: Yes.
Mr Mashigo: Fine.
[Silence]
Mr Mashigo: So here we have equal amounts.
Class: Yes.
247
Mr Mashigo: But the point is we have a nitric acid and a base. Now
one would expect that now.
[Silence]
Mr Mashigo: The colour change as in this stage should not take place.
Class: Yes.
Mr Mashigo: Unless one of these is diluted and the other one is
concentrated.
Class: Concentrated.
Mr Mashigo: Fine. Now let’s see.
[Silence]
Mr Mashigo: Let’s see as to whether it will…
[Silence]
Mr Mashigo: So if you look at that , instructions, nê?
Class: Yes.
Mr Mashigo: They are telling you that now?
[Silence]
Mr Mashigo: You must keep on adding until…
[Silence]
Mr Mashigo: Now I am resending you to point, point three. Carefully
pipette the diluted hydrochloric acid into test-tube one,
four and seven.
Class: Seven.
Mr Mashigo: Until the litmus paper turns purple. In other words now.
What is it that we add in test-tube one and, one, four and
seven? According to the instruction here we on test-tube
one, four and seven we must have the litmus paper and
then we pipette our chloric acid and stir frequently. If too
much acid is added and the little of the alkali is repeated
with an acid, manually changing temperature with
thermometer.
Class: Thermometer.
Mr Mashigo: Do we have a change in temperature here.
[Silence]
Mr Mashigo: now.
248
[laughter]
Mr Mashigo: So tell them what is the reading on the thermometer?
Learner: [Inaudible]
Learner: Beneath zero.
Mr Mashigo: Beneath zero.
[Silence]
Mr Mashigo: Let’s see. You can see here. What stuff is in there?
Learner: [Inaudible]
Mr Mashigo: [Inaudible] because at that time because [Inaudible].
What is that in it?
Learner: Acids.
Mr Mashigo: Acids.
Learner: Yes sir.
Mr Mashigo: What is that [Inaudible]? What is [Inaudible]?
[Silence]
Mr Mashigo: That’s it. Alright, so they are saying the temperature is
fifteen degrees Celsius. Now let’s stir on the mixture.
[Silence]
Mr Mashigo: [Inaudible]
[Laughter]
Mr Mashigo: Oh [Inaudible]
[Laughter]
Mr Mashigo: They said we should keep on stirring…
Class: Yes.
Mr Mashigo: And then when you stir what is that we will observe?
Class: The temperature changes.
Mr Mashigo: Temperature rises it means what?
Class: Exothermic.
[Silence]
Mr Mashigo: Alright, meanwhile while we are looking at that. Now the
other instruction here is to repeat the, the experiment and
add sulphuric acid to test, to, to find [Inaudible]
Class: [Inaudible]
Mr Mashigo: And the nitric acid.
249
Class: Acid.
Mr Mashigo: To test-tube three six and nine. So in other words now
let’s follow these to the last. Alright?
Class: Yes.
Mr Mashigo: Fine. What we do on test-tube, because now [Inaudible]
the test-tubes with me, on one four and seven.
[Silence]
Mr Mashigo: One, two, three, four, five, six.
[Silence]
Mr Mashigo: Let’s repeat it.
[Silence]
Mr Mashigo: For accuracy sake.
[Silence]
Mr Mashigo: Alright,. The instruction says that now on test-tube one,
four and seven which solution must be there?
Class: Hydrochloric acid.
Mr Mashigo: Of hydrochloric acid.
Class: Acid.
Mr Mashigo: Fine. Now, here is hydrochloric acid but now in this, in
this one, four and seven I’ll pour a little bit of it but now,
now we need to be accurate. I’ll have to improvise so that
, we can be a person to quickly work.
[Silence]
Mr Mashigo: I use this syringe so that I can measure accurately the
equal quantities.
Class: Quantities.
[silence]
Mr Mashigo: So we have hydrochloric acid.
Class: Acid.
[Silence]
Mr Mashigo: Alright. Now.
[Silence]
Mr Mashigo: On test-tube one.
Learner: Test-tube one.
250
[Silence]
[Laughter]
Mr Mashigo: And then on test-tube four.
Class: Four.
[Silence]
Mr Mashigo: And lastly on test-tube seven.
Class: Seven.
[Silence]
Mr Mashigo: Alright, I think you should understand one thing. That ,
whenever you perform an experiment always follow the
instructions.
Class: Instructions.
[Silence]
Mr Mashigo: As you will have seen my attempts were unsuccessful.
You remember?
Class: Yes.
Mr Mashigo: Fine. Now, we have hydrochloric acid in test-tube one,
four and seven.
Class: Seven.
Mr Mashigo: Fine. Now what else do they say here? They say a
solution of metal hydroxide. Take about five grams of
sodium hydroxide. Alright, now.
[Silence]
Mr Mashigo: Let’s make a solution of sodium hydroxide.
[Silence]
Mr Mashigo: Now you remember on test-tube one, four and seven
what acid do we have?
Class: Hydrochloric acid.
Mr Mashigo: Hydrochloric acid. Now, in that solutions we know that
now if we place a litmus paper the blue one will turn to
red.
Class: Red.
Mr Mashigo: Fine. Now in that solution we now add sodium hydrox..
Class: Hydroxide.
251
Mr Mashigo: Sorry, sodium hydroxide.
[Silence]
Mr Mashigo: So its test-tube one.
Class: One.
[Silence]
Mr Mashigo: And then four.
[Silence]
[Laughter]
Mr Mashigo: Ja I know this is for. I am looking at the quantity that is
there.
Class: Yes.
Mr Mashigo: And then also [Inaudible]
[Silence]
Mr Mashigo: Fine. Now.
[Silence]
Mr Mashigo: Let’s take a litmus paper. If you look at that , worksheet
they say that now look at the colour of the solution. Now
the one that we have here is potassium hydroxide.
Class: Hydroxide.
Mr Mashigo: Now potassium hydroxide and a metal hydroxide it’s
number two from the top or number two from the bottom.
Alright, now let’s drop it. , litmus paper.
[Silence]
Mr Mashigo: Unfortunately I have to cut it because I’m running out of
the blue litmus paper.
[Silence]
Mr Mashigo: That is in test-tube number one.
Class: One.
[Silence]
Mr Mashigo: With that [Inaudible] this will colour change.
Class: Now we see.
Mr Mashigo: Remember it’s a blue one. And then what do we have
here?
Class: Blue paper.
252
Mr Mashigo: We have an acid do you remember? Hydrochloric acid
and what?
Learner: and the potassium.
Mr Mashigo: And a potassium. Sodium hydroxide.
Class: Sodium hydroxide.
Mr Mashigo: Now, is there any colour change on the litmus paper?
Class: No.
Mr Mashigo: you get that?
Class: Yes.
Mr Mashigo: Fine. What does that tell you? About the acid that has
been poured in and the base?
Class: The base neutralised the acid.
Mr Mashigo: [Inaudible] advantages.
Class: Yes.
Mr Mashigo: Hence no effect on this. Why? Because the acidic
properties as well as the acidic as well as the base
properties have cancelled. In other words now, what we
have here is um, potassium hydroxide plus HCL and what
happens is that now this base that we have potassium
ions in the hydroxide ions. And this base we have
hydrogen protons and , the chloride ions. You get that?
Class: Yes.
Mr Mashigo: Now we know that now this one and that one will form a
salt, potassium chloride and this one and this one will
form water. You get that?
Class: Yes.
Mr Mashigo: Now water is neutral. When you say something is neutral
it is neither acidic nor basic.
Class: Basic.
Mr Mashigo: Remember?
Class: Yes.
Mr Mashigo: Fine. Now let’s see whether it’s the same situation on
test-tube number four. But if there is a change in colour
253
what would you expect or what would you, how would
you explain that?
[Silence]
Mr Mashigo: Again look at this.
Class: No change.
Mr Mashigo: There’s no change.
Class: Change.
Mr Mashigo: You get that?
Class: Yes.
Mr Mashigo: Fine. But now let’s look at number seven.
Class: Seven.
[silence]
Mr Mashigo: Look at this one. Any visible change?
Class: No.
Mr Mashigo: Fine. Now according to the instructional sheet indicate
any visible change in reaction.
Class: Reaction.
Mr Mashigo: So for the second one we start with hydrogen chloride
then state whether potassium hydroxide and nitrogen
chloride was there a change?
Class: No.
Mr Mashigo: Then write down that there’s not any visible change. It’s
like this. For this one, for potassium hydroxide and
hydrochloric acid then you write here. No change is,
there’s no change.
[Silence]
Mr Mashigo: Look at the chalkboard now. We have this and that,
alright?
Class: Yes.
Mr Mashigo: If there is a change you write whatever change, if there is
no change there is no change.
Class: Change.
Mr Mashigo: In the colour of litmus paper.
Class: Paper.
254
Mr Mashigo: If there is no col-, there is no colour change what does
that mean? It means that now this have neutralised. In
other words now the basic properties and the acidic
properties have neutralised each other by forming salt
and water.
Class: Water.
Mr Mashigo: Fine, now let’s take a same solution but then look at
when we add sulphuric acid.
Class: Acid.
Learner: Before we go on right.
Mr Mashigo: .
Learner: How do we always have to look at the litmus paper or are
there other solution that you help to take a reading?
Mr Mashigo: There are some other solutions that , can be used to tell
us whether a solution is acidic or basic.
Class: Basic.
Mr Mashigo: Like for instance now we have what we call indicators.
Like for instance now we have bromethymide blue. You
get that?
Class: Yes.
Mr Mashigo: And then we also have methide orange but , the fast test
and the easiest to want is the one where we use a litmus
paper because in lower classes we are told about the
litmus paper changing from blue to red, from red to blue.
Class: Blue.
Mr Mashigo: That is why we are sticking to that. Fine. Now on test-
tube two, five and eight.
[Silence]
Mr Mashigo: Repeat the experiment and add sulphuric acid in test-
tube two, five and eight.
Class: Eight.
Mr Mashigo: now, still with potassium hydroxide.
[Silence]
Mr Mashigo: Now, test-tube two.
255
[Silence]
Mr Mashigo: And then test-tube five.,
[Silence]
Mr Mashigo: and then test tube…
Class: Eight.
Mr Mashigo: Eight. So we’ll take this one as test-tube eight because
this one I have prepared the solution in. alright?
Class: Yes.
[Silence]
Mr Mashigo: But now this time what I must add is sulphuric acid.
Class: Acid.
Mr Mashigo: which is one of the strong acids?
Class: The strong acids.
[Silence]
Mr Mashigo: So here’s our sulphuric acid but people remember one
thing, you don’t have to handle these things with your
bare hands.
Class: Bare hands.
Mr Mashigo: Alright?
Class: Yes.
[Silence]
Mr Mashigo: Alright. Now on test-tube two.
[Silence]
Mr Mashigo: On test-tube five.
Class: Five.
[Silence]
Mr Mashigo: And we said this one that is test-tube number eight?
Class: Yes.
[Silence]
Mr Mashigo: Now what is the next thing that we do? To drop a litmus
paper?
Class: Paper
Mr Mashigo: You get that?
Class: Yes.
256
Mr Mashigo: Fine.
[Silence]
Mr Mashigo: Test-tube number two.
[Silence]
Mr Mashigo: look at what happens here.
Class: It changes.
Mr Mashigo: And then test-tube five.
[Silence]
Class: It change colour, it changes.
Mr Mashigo: Test-tube number eight.
Class: Eight.
Mr Mashigo: But now people understand one thing. We need to be
able to explain what we see.
Class: Yes.
Mr Mashigo: Now, what is it that you think makes that colour change to
occur?
Learner: Acid is more.
Mr Mashigo: So you are saying acid is more than the base.
Class: Base.
Mr Mashigo: What if I argue and say that the acid is stronger than the
base?
Class: Yes sir.
Mr Mashigo: Because we added the same amount.
Class: Amount.
Mr Mashigo: but what was in it that a base will neutralise an acid?
Class: Acid.
Mr Mashigo: And when it neutralises it, what does it do? It destroys the
acid.
Class: Destroys the acid.
Mr Mashigo: But on test-tube number two, five and eight did that
happen?
Class: No.
Learner: The acid which was stronger.
Mr Mashigo: Alright.
257
Learner: Than the base.
Mr Mashigo: So in other words now to explain what we see, the base
[Inaudible]. One is either the acid is stronger…
Class: Stronger.
Mr Mashigo: …than the base.
Class: Base.
Mr Mashigo: Or two, we did not pour equal quantities.
Class: Quantities.
Mr Mashigo: you might find that now what is more? Because the
colour changes from blue to red.
Class: Red.
Mr Mashigo: Between an acid and a base which one you think is
more?
Class: Acid.
Mr Mashigo: The acid isn’t it?
Class: Yes.
[silence]
Mr Mashigo: Alright. Now you can know to whatever changes that are
there. Correct?
Class: Yes.
Mr Mashigo: And then we can continue again. Now, , sometime I’ll give
you the notes.
Class: Yes.
Mr Mashigo: And then after the notes you will then be given the
homework so that you go and practice what we learnt
today.
Class: Yes sir.
Learner: [Inaudible]
[recording ends]
258
G.3: Class Observation - Mrs Mbele Researcher: This is the lesson observation of Mrs Mbele.
Mrs Mbele: Okay. Good morning boys and girls.
Class: Good morning ma’am.
Mrs Mbele: Right, I want to introduce to you ma’am Joseph. It’s Mrs
Joseph our district physical science facilitator. So she’s,
she has come here to observe how I’m learning. Okay?
Class: Yes ma’am.
Mrs Mbele: And remember we did give you the indemnity forms.
Class: Yes ma’am.
Mrs Mbele: You have submitted those indemnity forms, nê? She is
going to collect them. I’m going to give them to her. So
she’ll be sitting there at the back listening to the
conversation between me and you. Okay?
Class: Yes ma’am.
Mrs Mbele: Thank you very much. You can hand those in.
[Background noise]
Researcher: This lesson is done by…
Mrs Mbele: Mrs Magoda.
Researcher: Mrs Mbele Magoda.
Mrs Mbele: Yes.
[Background noise]
Mrs Mbele: Right, you have done acids and bases, nê?
Class: Yes ma’am.
Mrs Mbele: So I want you to tell me, , can you define an acid in terms
of [Inaudible] an acid, what is an acid? Kgotso?
Kgotso: Ma’am an acid is a proton donor.
Mrs Mbele: An acid is a proton donor.
[Background noise]
Mrs Mbele: What is a base? In terms of [Inaudible] again. Maiman?
Learner: It’s a proton acceptor.
Mrs Mbele: It’s a proton acceptor.
[Background noise]
259
Mrs Mbele: So an acid is a proton donor, a base is a proton acceptor.
Do you still remember in terms of conjugated bases, nê?
Whereby an acid is going to donate a proton and a base
is going to accept that proton. Right, uh, I want you also
to tell me, what is the difference or what is a ph? Let’s
talk of the ph, what is the ph? What is a ph scale? What
is the ph scale? Bongani?
Bongani: The ph scale is a measurement of an acid from a base
and how strong it is.
Mrs Mbele: It is an indication between a base and an acid, nê?
Learner: Yes.
Mrs Mbele: Whereby we know what is the ph. Can you please just tell
me the ph of a, an acid? What is the value of the ph of an
acid?
Learners: [Inaudible]
Mrs Mbele: The ph of an acid? Raise your hands. We are not in a
choir here.
Learner: I can’t hear what you’re saying to me.
Mrs Mbele: From less than seven and those are acids nê?
Class: Yes.
Mrs Mbele: And then in terms of classification of stronger acid and
weaker acid. Which one, which numbers, let’s say, let me
give you an acid of one, of ph of one, an acid of ph of
five. Which acid is the strongest? Between the one and
the five?
Learner: One.
Learner: One.
Mrs Mbele: Spark?
Learner: The one.
Mrs Mbele: One. One is the strongest acid, nê?
Class: Yes.
Mrs Mbele: And then we know that from seven upwards is the base,
nê?
Class: Yes.
260
Mrs Mbele: Right. We have done also the oxidation numbers, nê?
Class: Yes.
Mrs Mbele: Did we do the oxidation numbers?
Class: Yes ma’am.
Mrs Mbele: Yes, we’ve done them, nê?
Class: Yes.
Mrs Mbele: So I want you to give me the oxidation number of a,
ammonium. Not ammonia. Ammonium. NH. What will be
the oxidation number of ammonium?
[Background noise]
Mrs Mbele: [Inaudible] we check. Nitrogen is in which group?
[Background noise]
Mrs Mbele: Nitrogen?
[Background noise]
Mrs Mbele: Let me take out the periodic table to go to nitrogen.
Check nitrogen. In which group?
[Background noise]
Mrs Mbele: Nitrogen is in group five, nê?
Class: Yes.
Mrs Mbele: Therefore we know in a periodic table we have eight
groups, nê?
Class: Yes.
Mrs Mbele: So when we say how do we get? You say eight minus
…?
Class: Five, five, five.
Mrs Mbele: Therefore we get the oxidation number of what?
Class: Nitrogen.
Mrs Mbele: Of nitrogen. Therefore it’s what?
Class: Three.
Mrs Mbele: It’s a three.
Class: Yes.
Mrs Mbele: Five minus eight…
Class: Yes.
Mrs Mbele: Negative and then how many hydrogen do we have?
261
Class: Four.
Mrs Mbele: What is the oxidation number of hydrogen?
Class: One.
Mrs Mbele: Why do we say it’s one?
Class: Because it is in group one.
Mrs Mbele: Because it is in group one. Therefore the oxidation
number of this whole compound would be what?
Class: Plus one.
Mrs Mbele: It will. We’ve got minus three plus four. It’s gonna be plus
one. Okay?
Class: Yes.
Mrs Mbele: Right. We have done the acid. Now we are going to talk
of the redox reaction.
Class: Yes.
[Background noise]
Mrs Mbele: When we talk of redox reaction, that’s when now we talk
of reactions whereby the electron are transferred. Since
one …
Class: Yes.
Mrs Mbele: Here, remember in an acid we talk of protons but in terms
of reactions, redox reactions that’s where we talk of
electron transfer.
[Background noise]
Mrs Mbele: We talk of electron transfer and this redox, it’s an
oxidation and reduction reactions. Okay?
Class: Yes.
Mrs Mbele: So, we talk of oxidation. Let’s start with oxidation. When
we talk of oxidation, in oxidation remember we said its
electron, that’s where we have LEO which is lose of
electrons. [Inaudible] it loose electrons.
Class: Loose electrons.
Mrs Mbele: Therefore it is oxidation.
[Background noise]
Mrs Mbele: Okay?
262
Class: Yes.
Mrs Mbele: Loss of electrons is oxidation. Remember we are
explaining this word. Therefore that one is an oxidation
reaction whereby there is a loss of electrons. Always
remember LEO. Loss of electron oxidation. Okay?
Class: Yes.
Mrs Mbele: The other type is reduction.
[Background noise]
Mrs Mbele: When we talk of reduction that’s where we say GERRR… [Background noise]
Mrs Mbele: Gain electrons reductions. Easy?
Class: Easy.
Mrs Mbele: Right. I’m going to distribute to you the table whereby
now we explain the oxidising and the reducing agents. If it
loses the electrons it is the oxidation. In terms of , the
reducing ability or oxidising ability. Oxidation will be
paired with reducing agent, in terms of agents now.
Class: Yes.
Mrs Mbele: Do we get each other?
Class: Yes.
Mrs Mbele: Right. You can have a copy of this. Just pass one. This is
a table which shows the [Inaudible] reduction potentials.
[Background noise]
Mrs Mbele: So make it snappy that all of you, you do have that.
[Background noise]
Mrs Mbele: One for each. Just use one. So that is the table of the, the
potentials, the reducing potentials, nê? Which is B, which
is normally included in your information sheets. Right,
when we talk of oxidation, we said oxidation in turn, in
oxidation. Give one to Bongani. [Background noise]
Mrs Mbele: Someone else sit down.
[Laughter]
Mrs Mbele: I’ve seen that you are present.
263
[Laughter]
[Background noise]
Mrs Mbele: Right, when we talk of oxidation in terms of agents I said
it is the reducing agent. When I said it is the reducing
agent what do I mean? That means it is an electron
donor. [Inaudible]
Class: Yes.
Mrs Mbele: This one it’s a reducing…
[Background noise]
Mrs Mbele: …agent. So immediately when it donates electrons, it is
an electron donor. Okay?
Class: Yes.
Mrs Mbele: It’s a reducing agent. It is, it loss, it loses electrons, its
oxidation. Therefore if it is oxidation it is a reducing agent.
It is an electron donor. We are going to do an experiment
whereby you are going to see it practically. How are the
electrons lost? Okay?
Class: Yes.
Mrs Mbele: Right. Then this one reduction, which is GER, gain
electrons. Obvious, if this one is a reducing donor, this
one will be the what?
Class: Oxidising.
Mrs Mbele: Oxidising. It’s either oxidising, it’s an oxidising agent…
Class: Agent.
Mrs Mbele: Because what is it going to do? It is going to be a what?
An acceptor of electrons.
Class: Acceptor of electrons.
Mrs Mbele: I know we said this one it gains…
Class: Yes.
Mrs Mbele: …therefore the oxidising agent, don’t confuse yourself
with oxidation and oxidising agent, okay?
Class: Yes.
Mrs Mbele: Those are two different things. Right, I also have, , some
papers here whereby you are going to do an
264
investigation and an experiment. You still remember first
that you must make sure that you are in groups?
Class: Yes.
Mrs Mbele: So each and every group I’m going to give it a page
whereby you are going to do the first experiment. It is
experiment A. I have five glasses there that we will use to
do this experiment. Because we are short of equipment.
[Background noise]
Mrs Mbele: Right, everyone I want you to go in groups. Just make
sure you have two in a group. Alright then three in a
group.
[Background noise]
Mrs Mbele: Two in a group, nê? Because it’s gonna be impossible for
six people to be in one place.
[Background noise]
Mrs Mbele: Right, we are going to do the first experiment. This
investi-, , this experiment investigates the, the direct
transfer of electrons in oxidation and reduction reactions.
Do you still remember I said to you we are going to talk of
electrons transfer? I need…
Class: Yes.
Mrs Mbele: Right, this is what you are going to do experimentally.
The first thing that I’m going to do. I’m going, I’m going to
have a copper sulphate. Let me just remove this so that
you will know which experiment. We are at A. Method A.
In that box those are the apparatus, nê?
Class: Yes.
Mrs Mbele: We start with the first experiment. In the first experiment
we are going to have a beaker. Here is our beaker, okay?
Class: Yes.
Mrs Mbele: In this beaker I’m going to pour water.
[Water pouring into glass]
Mrs Mbele: Do you all see this water?
Class: Yes ma’am.
265
Mrs Mbele: Do you all see? This is water. I’m making a solution of
what do we call this?
Class: Copper sulphate.
Mrs Mbele: It’s a copper sulphate, nê?
Class: Yes.
Mrs Mbele: And then what colour is it?
Class: Blue.
Mrs Mbele: Let’s see whether it remains blue if we pour it in water.
One … two … say three! We have used a spatula to pour
three and then we stir in order to make a solution of
copper sulphate. Do you all see this?
Class: Yes.
Mrs Mbele: What colour is it?
Class: Blue.
Mrs Mbele: You must make sure that it dissolves, all of it dissolves in
this. Okay?
Class: Yes.
[Background noise]
Mrs Mbele: So we are doing it, it says we must half fill nê? Because
we have limited resources that’s why I’ve poured just a
little bit of a solution in this beaker.
[Background noise]
Mrs Mbele: Then there is an apparatus that is used to measure
temperature. We call that apparatus…?
Class: Thermometer.
Mrs Mbele: A thermometer. We are going to take a thermometer
according to the instructions. The instructions says, can I
hold a thermometer in this side?
Class: No.
Mrs Mbele: Why?
Class: Because [Inaudible]
Mrs Mbele: You raise your hand. This is not a choir. Because the, my
temperature is going to affect the temperature that is in
this thermometer okay?
266
Class: Yes.
Mrs Mbele: You hold it like this and then we are going to do what?
The instructions says we must measure the temperature
of the solution. [Background noise]
Mrs Mbele: Here is a thermometer. You see it so we are going to
measure the solution of this. Can one of you or two of
you come so that we verify the results? Two of you come,
one boy, one girl, come. To check the temperature.
[Background noise]
Mrs Mbele: Stand at that other side. Check the temperature and tell
them.
Learners: [Inaudible]
Mrs Mbele: Hmm?
[Background noise]
Learner: It becomes hotter [Inaudible]
Mrs Mbele: Make sure that both of you, you agree with what you are
seeing. That’s why I called two people.
Learner: We need to…
Mrs Mbele: And don’t manipulate it, nê? Please.
Learner: Look its hot here…
Mrs Mbele: Make it snappy.
Learner: It’s nine.
Mrs Mbele: You agree it’s nine?
Learner: Yes.
Mrs Mbele: The temperature is nine degrees Celsius, nê?
Class: Yes.
Mrs Mbele: In a copper solution, a copper sulphate solution, right.
The instruction says we must add, , excess zinc powder
in this.
[Background noise]
Mrs Mbele: This is zinc powder. This is zinc powder. Hence I’ve said
we have limited resources.
Class: Yes.
267
Mrs Mbele: So we are going to do it with limited resources. This is
zinc powder, so we are going to pour zinc powder…
[Background noise]
Mrs Mbele: …this is zinc powder.
[Background noise]
Mrs Mbele: After pouring a zinc powder it says you must do what?
Class: We must stir.
Mrs Mbele: We must stir it slowly…
Class: Slowly…
Mrs Mbele: …and carefully….
Class: Carefully…
Mrs Mbele: Nê?
Class: Yes.
[Background noise]
Mrs Mbele: Two boys come. A boy and a girl again. And they’re the
same ones that were here. Come quickly.
[Background noise]
Mrs Mbele: And you must carefully measure what? You must also
measure temperature, nê?
Learners: Yes.
Mrs Mbele: You write down the readings.
Learner: Yes.
[Background noise]
Mrs Mbele: It’s rising now you see it? It’s in thirteen.
Learner: Twelve.
Mrs Mbele: Twelve? The temperature now after stirring for the first
time, the temperature is what?
Class: Twelve.
Mrs Mbele: Twelve. Let’s, let’s get twelve here.
Learner: Twelve?
Mrs Mbele: I don’t know where you get your nineteen. Thereby it’s
twelve. The temperature that they are seeing here.
Class: Yes.
268
Mrs Mbele: Twelve degrees Celsius. And then it says read the
temperature regularly until no further temperature change
is observed. Remember at first the temperature was
what?
Class: Nine.
Mrs Mbele: Now because we have added zinc powder the
temperature has done what?
Class: Increased.
Mrs Mbele: It has increased. Right. And then we must do this up until
no temperature changes.
Class: Ooh.
Mrs Mbele: Okay?
Class: Yes.
Mrs Mbele: Until the temperature remains constant now. Come.
Come.
[Background noise]
Mrs Mbele: Stand this side so that you can also see it.
[Background noise]
Mrs Mbele: Yeah until it stops rising. You must tell them now it’s
rising to what? You must give them the readings, the
numbers.
[Background noise]
Learner: It’s rising.
Mrs Mbele: It’s still rising, okay. They are saying it is still rising.
[Background noise]
Learner: Ja, fourteen.
Mrs Mbele: It’s fourteen? Now it’s rising, it’s fourteen degrees, nê?
Class: Yes.
[Background noise]
Mrs Mbele: That means the reaction is still taking place.
[Background noise]
Mrs Mbele: It is still at fourteen?
Learner: Yes.
269
Mrs Mbele: They are saying it is still at fourteen. That means the
reaction has stopped now. [Inaudible]
Class: Yes.
Mrs Mbele: If the temperature is constant that means the reaction
equilibrium has been reached. [Inaudible]
Class: Yes.
Mrs Mbele: Equilibrium has been reached.
Class: Yes.
Mrs Mbele: So you can sit down, thank you. As this has happened we
must leave this. We filter the content or let the beaker
stand until all the insoluble material has settled. So we’ll
check your readings, nê?
Class: Yes.
Mrs Mbele: We will check again. We will just put this aside. We put
this aside and there are questions there because this also
serves as a worksheet. There are questions there that
needs to be answered by you. I need you to answer
these questions now. The first question. The solution
colour changed from what to what?
Class: Blue.
Mrs Mbele: The colour was what?
Class: Blue.
Mrs Mbele: And then it changed now to?
Class: Black.
Mrs Mbele: Greyish, it’s not black, it’s greyish.
Class: Greyish.
Mrs Mbele: Okay?
Class: Yes.
Mrs Mbele: To greyish. Right, the temperature rose from where to
where?
Class: From nine to twelve..
Mrs Mbele: Maybe if I’m a conductor of a choir you will sing like this.
Someone?
Learner: From nine degrees to fourteen degrees.
270
Mrs Mbele: Good boy. When you say from nine to fourteen I don’t
know what are you talking about. You should be specific.
It rose from nine degrees Celsius to fourteen degrees
Celsius, okay?
Class: Yes.
Mrs Mbele: Right, the reaction now, remember, as the temperature is
rising, what is liberated? What is released?
Class: [Inaudible]
Mrs Mbele: What is released. Will you raise your hands? What is
released? Talif?
Talif: Energy.
Mrs Mbele: Energy is released, nê?
Class: Yes.
Mrs Mbele: So if there is an exit of energy therefore the type of
reaction now is what? This is an exit one, we have done
this. We have done it. Mpho?
Mpho: It’s and exothermic reaction.
Mrs Mbele: It’s an exothermic reaction. Okay?
Class: Yes.
Mrs Mbele: It’s an exothermic reaction because energy has been
liberated. Remember I said exo - exit. Exit that is when
something leaves. Okay?
Class: Yes.
Mrs Mbele: So the temperature has done what? It has imprinted
[Inaudible] into the thermometer and rising the
thermometer. Therefore there is a release of energy
okay?
Class: Yes.
Mrs Mbele: Right, now we are going to do the second experiment.
Which is experiment B.
Learner: Yes.
Mrs Mbele: Whereby we are still going to use the solution of copper
sulphates but this one I’m going to do it. I’m going to do
this experiment.
271
[Background noise]
Mrs Mbele: Okay.
[Background noise]
Mrs Mbele: And I hope and believe that you have observed the
change in temperature whereby now we are going to
compare in this two the type of a reaction. Whether which
one was fast, which one was slow. We have done A, now
we go to B.
[Background noise]
Mrs Mbele: I’m preparing a solution of copper sulphate and this
solution of copper sulphate.
[Background noise]
Mrs Mbele: I must use my steel wool. You see this zinc rod? It’s dirty,
can you see it?
Class: Yes.
Mrs Mbele: So I must thoroughly clean it with a steel wool.
[Background noise]
Mrs Mbele: And after that and measure its mass carefully. You see
I’ve cleaned it, nê?
Class: Yes.
Mrs Mbele: This is a scale. Whereby it’s an electronic, electric scale.
It’s, it’s off. Now it’s on.
[Background noise]
Mrs Mbele: It’s an old scale. Oh my goodness, it’s on but it’s not
working.
[Laughter]
Mrs Mbele: We do have electricity mos and it was working in the
morning. Okay, nevertheless, because we don’t have a
scale, , hey, it’s frustrating me now.
[Background noise]
Mrs Mbele: This electricity council, there is no electricity.
[Background noise]
Mrs Mbele: Right, what we are going to do, nevertheless lets discuss
what was going to happen. Just check it if it decide to be
272
on because it’s an old scale. If you just see the writings
just tell me, we will measure this and do it practically. So,
what is going to happen is this. We are going to take this
zinc rod and measure the mass of it. Okay?
Class: Yes.
Mrs Mbele: After measuring the mass it will, let’s assume its fifty
gram because the, the mass it’s in grams. So it will be in
fifty grams, it’s before. Then we take it and put it in a
solution of copper sulphate. After measuring it, nê?
Class: Yes.
Mrs Mbele: We put it in a solution of copper sulphate and observe its
appearance every minute. We will observe its
appearance as point number three. Don’t rush to point
number four. You place the zinc plate in the copper
sulphate. Here it is what I’ve done and observe its
appearance every few fifteen minutes. Few minutes, then
you leave it in this solution for fifteen minutes. After
leaving it for, this solution for fifteen minutes, what is
going to happen is that you are going to rinse it carefully.
First in water. After rinsing it in water you are going to
rinse it in alcohol.
Class: Yes ma’am.
Mrs Mbele: Do you know alcohol?
Class: Yes.
Mrs Mbele: Think like ethanol, nê?
Class: Yes.
Mrs Mbele: You rinse it in alco- you, you start with water and then
you rinse it in alcohol. After rinsing it from water you take
into alcohol. After rinsing it in alcohol you let it dry.
Remember we measured it while it was dry nê?
Class: Yes.
Mrs Mbele: You let it dry. After it is dry you go again and measure its
mass. So that’s where you are going to see the
difference now. Then after you will see that okay, it has, if
273
you pour a small amount of the solution in the test tube
and bubble through both A and B. remember we have A,
which is what we have done.
Class: Yes.
Mrs Mbele: And we also have B, nê?
Class: Yes.
Mrs Mbele: We do what we bubble hydrogen sulphide gas. Hydrogen
sulphide gas it’s a gas that will lead us to open the
windows because it has a choking smell. We must open
the door when we prepare this the thing that we are going
to use. We are going to take iron sulphide and
hydrochloric acid.
[Background noise]
Mrs Mbele: We are going to take FeS plus HCl then they are going to
give us. Because we want what? We want the gas that is
going to be , , released. So the gas is going, this and this
is going to be HF + Iron chloride then balance your
reaction. Okay?
Class: Yes.
Mrs Mbele: So, this gas is prepared by the combination of these two
chemicals. In this with iron sulphide then we are going to
pour hydrochloric acid in it. After pouring hydrochloric
acid.
[Background noise]
Mrs Mbele: We pour, we pour hydrochloric acid here. You will see
there will be a reaction. Therefore a gas that is going to
be released we are going to take that gas. Remember it
says after fifteen minutes, although fifteen minutes have
not yet passed. We take it, this, this is a deliberate show.
We are going to take a gas from here and remember they
said we must bubble it here in both the solutions, nê?
Class: Yes.
274
Mrs Mbele: So I want you to tell me after we’ve bubbled it in both the
solutions, what is going to happen? You see there is a
change in this thing?
Class: I see.
Mrs Mbele: Do you see?
Class: Yes.
Mrs Mbele: The colour now here.
Class: Yes.
Mrs Mbele: The colour here. Where something which is like this
colour. What has accumulate, what do we think has
accumulated in this zinc plate?
Learner: [Inaudible]
Mrs Mbele: Remember here we have copper sulphate and it’s like a,
a magnet. So which magnet do you think has
accumulated here. Attached itself in this matter? I said we
have copper sulphate. We have C, , CuSO plus zinc and
I’m saying to you, a metal will be attracted to a metal. In
terms of magnets, nê?
Class: Yes.
Mrs Mbele: So now assume this is a magnet. So in this, in this two
things which one is going to attach itself there?
Class: Copper, copper.
Mrs Mbele: Copper, nê?
Class: Yes.
Mrs Mbele: Copper is going to be attracted there. So when copper is
attracted there it is no more, it is what? It is an ion. The
ions are just going to accumulate there and that is going
to surround this zinc metal. Okay?
Class: Yes.
Mrs Mbele: Alright. Let’s put this aside and do the hydrogen sulphide
gas. We are not using any fire, nê? There’s no fire in the
instructions, okay?
Class: Yes.
275
Mrs Mbele: There’s no fire. Please don’t tell me about the fire
because there is no fire here. [Background noise]
Mrs Mbele: I’m wondering whether this acid will also work. Because
immediately when it reacts I must bubble in both the
solutions. Let me put it in this one.
[Background noise]
Mrs Mbele: There’s no reaction.
[Background noise]
Mrs Mbele: It’s an old test tube.
[Laughter]
Mrs Mbele: No reaction.
[Background noise]
Mrs Mbele: Let’s try with this, uh, highly concentrated one.
[Background noise]
Mrs Mbele: In the meantime you must prepare yourselves for
answering the questions that are at the back. At the back
of that page there are questions there. Prepare yourself
to answer those questions. There you go.
[Background noise]
Mrs Mbele: And put people, you must also notice hey, you must also
notice the rate between the reaction that took place in A
and the reaction that is going to take place in B. Okay?
Class: Yes.
Mrs Mbele: You are also going to notice that.
[Background noise]
Mrs Mbele: So you are going to tell me. Immediately when you see
the bubbles which you should know that something is
happening. [Background noise]
Mrs Mbele: So hold it upwards.
[Background noise]
Mrs Mbele: You will tell me in terms of the rate which one was fast,
which one was slow?
276
[Background noise]
Mrs Mbele: Do you see the bubbles?
Class: Yes.
[Background noise]
Mrs Mbele: Oh, it’s very slow.
[Background noise]
Mrs Mbele: Even the bubbles. Let me put it here so that you can see
the bubbles.
[Background noise]
Mrs Mbele: And also notice any colour changes, nê?
Class: Yes.
[Background noise]
Mrs Mbele: [Inaudible] [Background noise]
Mrs Mbele: I want you to see the colour changing. More especially in
this one. Remember it was blue, nê?
Class: Yes.
Mrs Mbele: So you’ll notice the colour change and you will tell me
which colour are you seeing now? Hence I was saying to
use a little bit it’s better than to use…
[Background noise]
Mrs Mbele: It’s changing.
Class: Yes.
Mrs Mbele: But slowly, nê? So if you compared the reaction in A and
the reaction in B you will notice that this one is more
faster and that one we are still seeing that colour nê?
Class: Yes.
Mrs Mbele: So in this one you can see now it becoming, this blue is
becoming uh…
Class: Yes.
Mrs Mbele: …much lighter.
Class: It is.
Mrs Mbele: So I will explain to you what has happened. This
experiment will carry it in two ways. What has happened
277
is that in A the reaction is fast and the reaction is fast,
there is a rise in temperature. And when there is a rise in
temperature we know that energy is being what?
Released.
Class: Yes.
Mrs Mbele: And if energy is released that the type of a reaction that is
taking place is what? It’s exothermic reaction. Remember
the colour its blue here nê?
Class: Yes.
Mrs Mbele: It was blue. Is it still that blue?
Class: No.
Mrs Mbele: It’s changing into which colour?
Class: Lighter … blue … powder blue.
Mrs Mbele: Hmm?
Class: Powder blue.
Mrs Mbele: It is changing. It is fading like it’s, it’s becoming in a water
of a colour nê?
Class: Yes.
Mrs Mbele: It is becoming greyish. Then it, this indicates that the
copper ions have disappeared here, okay?
Class: Yes.
Mrs Mbele: So immediately when the, the, the colour changes it
shows that the copper ions have disappeared. We are no
more going to say it’s a copper sulphate because we
know the colour of a copper sulphate is blue. So
immediately when we bubble that gas and it changes the
colour we should know that the copper ions, which are
the hydrated copper ions have chan- have done what?
They have disappeared. Because the colour now has
faded. Okay?
Class: Yes.
Mrs Mbele: Right. In B now what a, what, what could have happened
that in B after we’ve measured the mass. What we are
going to observe is that the mass in a zinc plate was
278
going to increase. Remember there was that copper
which was attaching itself there. [Inaudible] except it was
not there. So immediately if something has added here it
is going to do what? It is going to affect the mass.
Class: Yes.
Mrs Mbele: So after it has affected the mass, the mass of the zinc is
going to increase and the mass of the zinc have
increased. What is going to happen is that there is going
to be a white precipitate that you are going to observe. So
unfortunately it didn’t happen as, it didn’t uh, we didn’t
see it. But if you can check you can see that those white
substances which are found in this zinc, that is a white
precipitate that is going to be formed here. Then this, this,
this thing is going to reform in this solution when we, we
put a zinc plate. It was going to be clearly seen. Mhm.
[Inaudible] It’s like rotten eggs if you can the gas.
[Background noise]
Mrs Mbele: Right, we were going to see a white precipitate form
when the hydrogen sulphide is bubbled. But
unfortunately, but if you can come. Four people come,
four come, you will see something whitish which is a
white precipitate. Come, come quickly.
[Background noise]
Mrs Mbele: Just at the bottom of this. You see? There are some
things which are white which is the precipitate. A white
precipitate.
Learner: Good.
Mrs Mbele: If we take this and look just beneath it…
Learner: Ja.
Mrs Mbele: …you will see white things here. What [Inaudible]
understand. You will see the biggest thing, the white
precipitate, okay?
Class: Yes.
[Background noise]
279
Mrs Mbele: So this shows us [Inaudible] the zinc metal now has
changed. Remember here we said this copper in copper
sulphate, it has particles move, it has faded away. So in
immediate when it moves what is it going to do? We are
going to have what we call, this is going to fade and zinc
will have a zinc sulphate. And that copper ions.
Class: Yes.
Mrs Mbele: And we also have the copper ions, okay? Right, so the
zinc metal changes to zinc ion by losing two electrons. So
I want you to tell me if the zinc loses therefore it is what?
From what we have studied today? Zinc is going to have
a precipitate and a zinc metal, zinc is going to change
into zinc ions. When we talk of zinc ions it has two ions.
[Inaudible]
Class: Yes.
Mrs Mbele: Therefore it is going to lose two electrons. Here is a zinc.
Zinc has changed into zinc ions and when it has changed
into zinc ion it los- it loses two electrons. Those two
electrons are going to be gained by what?
Class: The copper…
Mrs Mbele: Remember we are talking of two metals. A zinc and a
copper. So if zinc loses two electrons, which metal is
going to gain the two electrons?
Class: Copper.
Mrs Mbele: Copper. Is it?
Class: Yes.
Mrs Mbele: Right. Zinc is going to lose two electrons, therefore
copper is gain two electrons. So the manner in which we
write it, copper remember we had this. In this one in the
aqua solutions. In aqua solutions that’s where we find the
ions situated. So here we have copper ions. We said zinc
is going to lose how many electrons?
Class: Two.
280
Mrs Mbele: Two electrons. So if zinc lose two electrons those two
electrons are going to be gained by copper. Okay?
Class: Yes.
Mrs Mbele: And then immediately when they are gained by copper
that’s where we are going to have what? A copper metal
which is a solid. Do you get me?
Class: Yes.
Mrs Mbele: Zinc is going to lose two electrons. If it loses two
electrons those electrons are going to be gained by
copper. The copper ions are going to gain two electrons
to give us a copper. Copper which is a metal. I don’t know
whether do you understand me?
Class: Yes we do.
Mrs Mbele: Right, now this one because it has uh, lost two electrons,
the losing of electrons it’s what? This is oxidation. So this
one because it has gained the electrons, we will call it
what?
Class: Electron…
Mrs Mbele: Reduction. [Inaudible]
Class: Yes.
Mrs Mbele: Reduction, so if reduction has taken place the overall
reaction when we are now to write the overall, which is
the net reaction, what we are going to do, we are going to
do this. We have what? Copper ion, so we have zinc. So
it will be zinc plus copper two ions giving us, this is
common so I will cancel this. Okay?
Class: Yes.
Mrs Mbele: Then we will have what this side we have what? Zinc ions
plus copper. This is the final reaction.
[Background noise]
Mrs Mbele: Remember we’re talking of a zinc-copper mater- , ,
metals. So what is happening is this, the two electrons
are, remember we talk of electrons transfer. So the
electrons have been transferred from zinc to copper, not
281
from copper to zinc. So if you check in your , standard
reduction potential. You see that?
Class: Yes.
Mrs Mbele: Check in that. Just use it to cancel, to underline where
you see copper with two electrons. Now I’m also teaching
you on how to use this table. Copper with two electrons.
Did you find it?
Class: Yes.
Mrs Mbele: Copper with two electrons?
Learner: Yes.
Mrs Mbele: Check where is zinc with two electrons.
[Background noise]
Mrs Mbele: You check zinc with two electrons.
Learner: Yes.
Mrs Mbele: Check zinc with two electrons.
[Background noise]
Mrs Mbele: Did you find that?
Class: Yes.
Mrs Mbele: Right, if you look at this table, where is zinc with two
electrons. No that’s still okay. It’s up there, ja, I’ve
underlined them. So as we said that zinc loses the
electrons, nê?
Class: Yes.
Mrs Mbele: It is oxidation. So you check. Do you still remember at the
site? If you look in this table, nê? This, this arrows, this
one it indicates that means from here to there, it’s a
increasing of oxidising ability. From that other side on
your right hand side it’s an increasing reducing ability. I
want you now to tell me in terms of uh, oxidising ability
and reducing ability, between this me-, copper and zinc,
which one is undergoing , which one is the reducing
agent? Or have a reducing ability? Which one has that
oxidising ability? Between the two?
[Background noise]
282
Mrs Mbele: Okay, which one is the oxidising agent? Between the two,
which one is the reducing agent? Mpho?
Mpho: The copper ion is the causing oxidation.
Mrs Mbele: Heh?
Mpho: Its oxidising I believe copper.
Mrs Mbele: Copper? Remember is reduction from this reduction is
what?
Mpho: [Inaudible]
Mrs Mbele: Oxidising. I said reduction it goes with oxidising and then
oxidation it goes with reducing agent. So if you check in
this table, this table clearly indicates to you. You check,
let’s go to zinc. Do you see zinc?
Class: Yes.
Mrs Mbele: So the arrow, the upper part of the arrow, it shows the
strongest what? It shows the strongest reducing.
[Inaudible]
Class: Yes.
Mrs Mbele: It shows the strongest reducing ability. Therefore zinc,
which one between copper and zinc shows the strongest
reducing ability.
Class: Copper?
Mrs Mbele: Check, check that table. Maiman?
Maiman: Zinc.
Mrs Mbele: Zinc, it’s where the strongest reducing ability is situated.
Class: Yes.
Mrs Mbele: Therefore, when you are asked in exam which one? You
are going to be given this table. As I am teaching you
now, you should know it’s not only between these two.
Any metal can be given. You can be given iron, you can
be given silver and uh, magnesium. You can be given
any but you need to do is to know how to use this table
and this table you have four, four B. There is also four A.
Okay? So you just check from the side. If I have the
strongest reducing abilities zinc being the part of the
283
strongest , reducing ability. That means the one at the
bottom will be what? It will have the strongest oxidising
ability. As we said that oxidation goes with reducing, not
with reduction, with reducing. Reduction goes with
oxidising. Okay?
Class: Yes.
Mrs Mbele: That’s how it is [Inaudible]. So now let’s go to the
questions also at the back. These questions are referring
to experiment number B which is experiment number two.
Remember we had a copper sulphate solution which is
this one nê?
Class: Yes.
Mrs Mbele: This is experiment number B. in experiment number B, ag
man, , we had experiment number A which is this one.
Class: Yes.
Mrs Mbele: And we have experiment number B. it says to you, the
colours of the solution changed from blue to what? Which
colour do you see?
Class: [Inaudible]
Mrs Mbele: It’s a lightish blue to greyish. Others are saying greyish.
Right, that’s correct. The mass of zinc plate I explained to
you. Did it decrease or did it increase?
Class: Increased.
Mrs Mbele: It increased. Remember there was a deposit of copper in
that zinc plate. Okay?
Class: Yes.
Mrs Mbele: Right. A red-brown layer off copper was going to be
formed. Remember the acid, I even showed you there
was that something that was rusty. So it was going to be
a red-brown going to be attracted to zinc. Okay?
Class: Yes.
Mrs Mbele: Thank you. Now I want you to ask me any questions
based on this experiment. That we have done. [Background noise]
284
Mrs Mbele: I explained to you what you have to expect so I want you
to tell me. Or should I ask you? Ask me questions based
on this experiments. Bongani?
Bongani: I want to know why zinc is rinsed with water first…
Mrs Mbele: What?
Bongani: …and then we have to rinse it again in alcohol?
Mrs Mbele: Bongani is asking why do we have to rinse zinc in water
and rinse it again in alcohol. Why?
[Background noise]
Mrs Mbele: Why? Anyone who can answer that? Bongani is asking
why do we have to rinse? Remember I said this zinc
metal, nê? We rinse it in water. After rinsing it in water we
are going to rinse in alcohol and dry it. Isn’t it? So he
wants to know why? The, the, the answer to, to this why
will be to remove the impurities that will be accumulating
this plate. We are removing the impurities that will be
accumulating in this zinc plate. Hence if we can remove
them with a steel wool we are going to be increasing the
mass of this zinc plate. So water had no effect it just
cleans. Okay?
Class: Yes.
Mrs Mbele: Are you all happy?
Class: Yes.
Mrs Mbele: Any other questions?
[Background noise]
Mrs Mbele: Enige vrae?
[Background noise]
Mrs Mbele: Calvin?
Calvin: No ma’am, if uh, you can take the zinc uh, plate…
Mrs Mbele: Mhmm.
Calvin: …then for a normal time on the catching of the copper be
more? Whereby the copper be attracted to the zinc plate?
Mrs Mbele: Ja, it will be more visible. It will be more visible. Sandile?
Sandile: Ma’am [Inaudible] copper, its copper was this [Inaudible]
285
Mrs Mbele: In experiment B?
Sandile: Yes.
Mrs Mbele: Okay. I said to you the copper was going to be deposited
into a zinc. What happens is that those people who were
in front if you look, if you look at it you are going to, to see
that it’s just, it’s a piece that is not happening. As we
expected it to happen. In experiment B the copper, this
was going to change the colour, so as I was saying that
those ions that are in this copper solution, copper
sulphate solution. We’re going to do what? The copper
ions were going to fade away. Hence we’re going to have
a greyish colour.
Sandile: [Inaudible] those electrons [Inaudible]
Mrs Mbele: Remember in a test tube we don’t have the electrons. It’s
a gas that is bubbled. So immediately when this gas, it’s
like when you do tea. You take water and the teabag, nê?
Class: Yes.
Mrs Mbele: That solution, immediately when you put a teabag in that
water you are going to have another colour. You can’t say
its water. The, because you put in a teabag. The colour of
the water is going to fade away and then you are going to
have a new thing which is called what? Water.
Class: Tea.
Mrs Mbele: Tea, ja I mean to say it. That is what I am trying to explain
to you. It’s water in, it’s, it’s copper sulphate in this, in this
[Inaudible] but immediately when you add, you bubble
hydrogen sulphide gas. It is changing now, we are no
more going to call it , copper sulphate. It’s like water, here
is water. You take a teabag you put a teabag here. The
colour of the water is going to do what?
Class: Change.
Mrs Mbele: It’s going to change. You are going to have a new thing
now which is tea. So this is what also happens here. Any
question?
286
[Background noise]
Learner: The thing I want to know, is it necessary to put in the
copper sulphate?
Mrs Mbele: Yes, this is the solution which indicates to us. It gives us
direction as it shows that it is going to accept the
electrons. Hence in both of them we have used, in A and
in B, we have used copper sulphate. It’s necessary to use
it.
Learner: Is it because they [Inaudible]
Mrs Mbele: Alright. What are, what is going to happen is this. I’m
going to give you a worksheet containing the questions
based on what we have done and on what I’ve explained
to you. And I want it tomorrow. Okay?
Class: Yes.
Mrs Mbele: Thank you. Class rep you will come to me and collect the
worksheets.
[Recording ends]
