CHEMISTRY HANDBOOK - Symbiosis International School

SYMBIOSIS INTERNATIONAL SCHOOL,

PUNE, INDIA

CHEMISTRY HANDBOOK

Contents

Introduction 2

3

4

Aims

Assessment objectives

Syllabus

5

Syllabus outline

7

Assessment

10

22

27

Assessment outline—SL

Assessment outline—HL

External assessment

Internal assessment

The group 4 project

132

Appendices

180

Sample Question Papers

Extended Essay Sample

IA sample

Resources 193

8

1

Introduction

Aims

Group 4 aimsThrough studying biology, chemistry or physics, students should become aware of how scientists work and communicate with each other. While the scientific method may take on a wide variety of forms, it is the emphasis on a practical approach through experimental work that characterizes these subjects.

The aims enable students, through the overarching theme of the Nature of science, to:

1. appreciate scientific study and creativity within a global context through stimulating and challengingopportunities

2. acquire a body of knowledge, methods and techniques that characterize science and technology

3. apply and use a body of knowledge, methods and techniques that characterize science and technology

4. develop an ability to analyse, evaluate and synthesize scientific information

5. develop a critical awareness of the need for, and the value of, effective collaboration andcommunication during scientific activities

6. develop experimental and investigative scientific skills including the use of current technologies

7. develop and apply 21st century communication skills in the study of science

8. become critically aware, as global citizens, of the ethical implications of using science and technology

9. develop an appreciation of the possibilities and limitations of science and technology

10. develop an understanding of the relationships between scientific disciplines and their influence onother areas of knowledge.

2

Introduction

Assessment objectives

The assessment objectives for biology, chemistry and physics reflect those parts of the aims that will be formally assessed either internally or externally. These assessments will centre upon the nature of science. It is the intention of these courses that students are able to fufill the following assessment objectives:

1. Demonstrate knowledge and understanding of:

a. facts, concepts, and terminology

b. methodologies and techniques

c. communicating scientific information.

2. Apply:

a. facts, concepts, and terminology


c. methods of communicating scientific information.

3. Formulate, analyse and evaluate:

a. hypotheses, research questions and predictions


c. primary and secondary data

d. scientific explanations.

4. Demonstrate the appropriate research, experimental, and personal skills necessary to carry outinsightful and ethical investigations.

3

Syllabus

Syllabus outline

Syllabus component Recommended teaching hours

SL HL

Core1. Stoichiometric relationships

2. Atomic structure

3. Periodicity

4. Chemical bonding and structure

5. Energetics/thermochemistry

6. Chemical kinetics

7. Equilibrium

8. Acids and bases

9. Redox processes

10. Organic chemistry

11. Measurement and data processing

9513.5

6

6

13.5

9

7

4.5

6.5

8

11

10

Additional higher level (AHL)12. Atomic structure

13. The periodic table—the transition metals

14. Chemical bonding and structure

15. Energetics/thermochemistry

16. Chemical kinetics

17. Equilibrium

18. Acids and bases

19. Redox processes

20. Organic chemistry

21. Measurement and analysis

602

4

7

7

6

4

10

6

12

2

OptionA. Materials

B. Biochemistry

C. Energy

D. Medicinal chemistry

1515

15

15

15

2525

25

25

25

4

Syllabus outline

Syllabus component Recommended teaching hours

SL HL

Practical scheme of workPractical activities

Individual investigation (internal assessment—IA)

Group 4 project

4020

10

10

6040

10

10

Total teaching hours 150 240

The recommended teaching time is 240 hours to complete HL courses and 150 hours to complete SL courses as stated in the document General regulations: Diploma Programme (2011) (page 4, Article 8.2).

5

Assessment

Assessment outline—SL

First assessment 2016

Component Overall weighting (%)

Approximate weighting of objectives (%)

Duration (hours)

1+2 3

Paper 1 20 10 10 ¾

Paper 2 40 20 20 1¼

Paper 3 20 10 10 1

Internal assessment

20 Covers objectives 1, 2, 3 and 4 10

6

Assessment

Assessment outline—HL

First assessment 2016

Component Overall weighting (%)

Approximate weighting of objectives (%)

Duration (hours)

1+2 3

Paper 1 20 10 10 1

Paper 2 36 18 18 2¼

Paper 3 24 12 12 1¼

Internal assessment

20 Covers objectives 1, 2, 3 and 410

7

Assessment

External assessment

Detailed markschemes specific to each examination paper are used to assess students.

External assessment details—SL

Paper 1Duration: 3/4 hourWeighting: 20%Marks: 30• 30 multiple-choice questions on core, about 15 of which are common with HL.

• The questions on paper 1 test assessment objectives 1, 2 and 3.

• The use of calculators is not permitted.

• Students will be provided with a periodic table.

• No marks are deducted for incorrect answers.

Paper 2Duration: 1¼ hoursWeighting: 40%Marks: 50• Short-answer and extended-response questions on core material.


• The use of calculators is permitted. (See calculator section on the OCC.)

• A chemistry data booklet is to be provided by the school.

Paper 3Duration: 1 hourWeighting: 20%Marks: 35• This paper will have questions on core and SL option material.

• Section A: one data-based question and several short-answer questions on experimental work.

• Section B: short-answer and extended-response questions from one option.




8

External assessment

External assessment details—HL

Paper 1Duration: 1 hourWeighting: 20%Marks: 40• 40 multiple-choice questions on core and AHL, about 15 of which are common with SL.


• The use of calculators is not permitted.

• Students will be provided with a periodic table.

• No marks are deducted for incorrect answers.

Paper 2Duration: 2¼ hoursWeighting: 36%Marks: 95• Short-answer and extended-response questions on the core and AHL material.




Paper 3Duration: 1¼ hoursWeighting: 24%Marks: 45• This paper will have questions on core, AHL and option material.

• Section A: one data-based question and several short-answer questions on experimental work.

• Section B: short-answer and extended-response questions from one option.




9

Assessment

Internal assessment

Purpose of internal assessmentInternal assessment is an integral part of the course and is compulsory for both SL and HL students. It enables students to demonstrate the application of their skills and knowledge, and to pursue their personal interests, without the time limitations and other constraints that are associated with written examinations. The internal assessment should, as far as possible, be woven into normal classroom teaching and not be a separate activity conducted after a course has been taught.

The internal assessment requirements at SL and at HL are the same. This internal assessment section of the guide should be read in conjunction with the internal assessment section of the teacher support materials.

Guidance and authenticityThe work submitted for internal assessment must be the student’s own work. However, it is not the intention that students should decide upon a title or topic and be left to work on the internal assessment component without any further support from the teacher. The teacher should play an important role during both the planning stage and the period when the student is working on the internally assessed work. It is the responsibility of the teacher to ensure that students are familiar with:

• the requirements of the type of work to be internally assessed

• the IB animal experimentation policy

• the assessment criteria—students must understand that the work submitted for assessment mustaddress these criteria effectively.

Teachers and students must discuss the internally assessed work. Students should be encouraged to initiate discussions with the teacher to obtain advice and information, and students must not be penalized for seeking guidance. As part of the learning process, teachers should read and give advice to students on one draft of the work. The teacher should provide oral or written advice on how the work could be improved, but not edit the draft. The next version handed to the teacher must be the final version for submission.

It is the responsibility of teachers to ensure that all students understand the basic meaning and significance of concepts that relate to academic honesty, especially authenticity and intellectual property. Teachers must ensure that all student work for assessment is prepared according to the requirements and must explain clearly to students that the internally assessed work must be entirely their own. Where collaboration between students is permitted, it must be clear to all students what the difference is between collaboration and collusion.

All work submitted to the IB for moderation or assessment must be authenticated by a teacher, and must not include any known instances of suspected or confirmed academic misconduct. Each student must confirm that the work is his or her authentic work and constitutes the final version of that work. Once a student has officially submitted the final version of the work it cannot be retracted. The requirement to confirm the authenticity of work applies to the work of all students, not just the sample work that will be submitted to the IB for the purpose of moderation. For further details refer to the IB publication Academic honesty (2011), The Diploma Programme: From principles into practice (2009) and the relevant articles in General regulations: Diploma Programme (2011).

10

Internal assessment

Authenticity may be checked by discussion with the student on the content of the work, and scrutiny of one or more of the following:

• the student’s initial proposal

• the first draft of the written work

• the references cited

• the style of writing compared with work known to be that of the student

• the analysis of the work by a web-based plagiarism detection service such as http://www.turnitin.com.

The same piece of work cannot be submitted to meet the requirements of both the internal assessment and the extended essay.

Group workEach investigation is an individual piece of work based on different data collected or measurements generated. Ideally, students should work on their own when collecting data. In some cases, data collected or measurements made can be from a group experiment, provided each student collected his or her own data or made his or her own measurements. In chemistry, in some cases, group data or measurements may be combined to provide enough for individual analysis. Even in this case, each student should have collected and recorded their own data and they should clearly indicate which data are theirs.

It should be made clear to students that all work connected with the investigation should be their own. It is therefore helpful if teachers try to encourage in students a sense of responsibility for their own learning so that they accept a degree of ownership and take pride in their own work.

Time allocationInternal assessment is an integral part of the chemistry course, contributing 20% to the final assessment in the SL and the HL courses. This weighting should be reflected in the time that is allocated to teaching the knowledge, skills and understanding required to undertake the work, as well as the total time allocated to carry out the work.

It is recommended that a total of approximately 10 hours of teaching time for both SL and HL should be allocated to the work. This should include:

• time for the teacher to explain to students the requirements of the internal assessment

• class time for students to work on the internal assessment component and ask questions

• time for consultation between the teacher and each student

• time to review and monitor progress, and to check authenticity.

Safety requirements and recommendationsWhile teachers are responsible for following national or local guidelines, which may differ from country to country, attention should be given to the guidelines below, which were developed for the International Council of Associations for Science Education (ICASE) Safety Committee by The Laboratory Safety Institute (LSI).

11

Internal assessment

It is a basic responsibility of everyone involved to make safety and health an ongoing commitment. Any advice given will acknowledge the need to respect the local context, the varying educational and cultural traditions, the financial constraints and the legal systems of differing countries.

The Laboratory Safety Institute’s Laboratory Safety Guidelines ...40 suggestions for a safer lab

Steps Requiring Minimal Expense1. Have a written health, safety and environmental affairs (HS&E) policy statement.

2. Organize a departmental HS&E committee of employees, management, faculty, staff and studentsthat will meet regularly to discuss HS&E issues.

3. Develop an HS&E orientation for all new employees and students.

4. Encourage employees and students to care about their health and safety and that of others.

5. Involve every employee and student in some aspect of the safety program and give each specificresponsibilities.

6. Provide incentives to employees and students for safety performance.

7. Require all employees to read the appropriate safety manual. Require students to read the institution’s laboratory safety rules. Have both groups sign a statement that they have done so, understand thecontents, and agree to follow the procedures and practices. Keep these statements on file in thedepartment office.

8. Conduct periodic, unannounced laboratory inspections to identify and correct hazardous conditionsand unsafe practices. Involve students and employees in simulated OSHA inspections.

9. Make learning how to be safe an integral and important part of science education, your work, andyour life.

10. Schedule regular departmental safety meetings for all students and employees to discuss the resultsof inspections and aspects of laboratory safety.

11. When conducting experiments with hazards or potential hazards, ask yourself these questions:

– What are the hazards?

– What are the worst possible things that could go wrong?

– How will I deal with them?

– What are the prudent practices, protective facilities and equipment necessary to minimize therisk of exposure to the hazards?

12. Require that all accidents (incidents) be reported, evaluated by the departmental safety committee,and discussed at departmental safety meetings.

13. Require every pre-lab/pre-experiment discussion to include consideration of the health and safetyaspects.

14. Don’t allow experiments to run unattended unless they are failsafe.

15. Forbid working alone in any laboratory and working without prior knowledge of a staff member.

16. Extend the safety program beyond the laboratory to the automobile and the home.

17. Allow only minimum amounts of flammable liquids in each laboratory.

18. Forbid smoking, eating and drinking in the laboratory.

19. Do not allow food to be stored in chemical refrigerators.

12

Internal assessment

20. Develop plans and conduct drills for dealing with emergencies such as fire, explosion, poisoning,chemical spill or vapour release, electric shock, bleeding and personal contamination.

21. Require good housekeeping practices in all work areas.

22. Display the phone numbers of the fire department, police department, and local ambulance either on or immediately next to every phone.

23. Store acids and bases separately. Store fuels and oxidizers separately.

24. Maintain a chemical inventory to avoid purchasing unnecessary quantities of chemicals.

25. Use warning signs to designate particular hazards.

26. Develop specific work practices for individual experiments, such as those that should be conductedonly in a ventilated hood or involve particularly hazardous materials. When possible most hazardousexperiments should be done in a hood.

Steps Requiring Moderate Expense27. Allocate a portion of the departmental budget to safety.

28. Require the use of appropriate eye protection at all times in laboratories and areas where chemicalsare transported.

29. Provide adequate supplies of personal protective equipment—safety glasses, goggles, face shields,gloves, lab coats and bench top shields.

30. Provide fire extinguishers, safety showers, eye wash fountains, first aid kits, fire blankets and fumehoods in each laboratory and test or check monthly.

31. Provide guards on all vacuum pumps and secure all compressed gas cylinders.

32. Provide an appropriate supply of first aid equipment and instruction on its proper use.

33. Provide fireproof cabinets for storage of flammable chemicals.

34. Maintain a centrally located departmental safety library:

– “Safety in School Science Labs”, Clair Wood, 1994, Kaufman & Associates, 101 Oak Street,Wellesley, MA 02482

– “The Laboratory Safety Pocket Guide”, 1996, Genium Publisher, One Genium Plaza, Schnectady, NY

– “Safety in Academic Chemistry Laboratories”, ACS, 1155 Sixteenth Street NW, Washington, DC 20036

– “Manual of Safety and Health Hazards in The School Science Laboratory”, “Safety in the School Science Laboratory”, “School Science Laboratories: A guide to Some Hazardous Substances” Council of State Science Supervisors (now available only from LSI.)

– “Handbook of Laboratory Safety”, 4th Edition, CRC Press, 2000 Corporate Boulevard NW, Boca Raton, FL 33431

– “Fire Protection Guide on Hazardous Materials”, National Fire Protection Association, Batterymarch Park, Quincy, MA 02269

– “Prudent Practices in the Laboratory: Handling and Disposal of Hazardous Chemicals”, 2nd Edition, 1995

– “Biosafety in the Laboratory”, National Academy Press, 2101 Constitution Avenue, NW, Washington, DC 20418

– “Learning By Accident”, Volumes 1-3, 1997-2000, The Laboratory Safety Institute, Natick, MA 01760

(All are available from LSI.)

13

Internal assessment

35. Remove all electrical connections from inside chemical refrigerators and require magnetic closures.

36. Require grounded plugs on all electrical equipment and install ground fault interrupters (GFIs) whereappropriate.

37. Label all chemicals to show the name of the material, the nature and degree of hazard, the appropriate precautions, and the name of the person responsible for the container.

38. Develop a program for dating stored chemicals and for recertifying or discarding them afterpredetermined maximum periods of storage.

39. Develop a system for the legal, safe and ecologically acceptable disposal of chemical wastes.

40. Provide secure, adequately spaced, well ventilated storage of chemicals.

Using assessment criteria for internal assessmentFor internal assessment, a number of assessment criteria have been identified. Each assessment criterion has level descriptors describing specific achievement levels, together with an appropriate range of marks. The level descriptors concentrate on positive achievement, although for the lower levels failure to achieve may be included in the description.

Teachers must judge the internally assessed work at SL and at HL against the criteria using the level descriptors.

• Assessment criteria are the same for both SL and HL.

• The aim is to find, for each criterion, the descriptor that conveys most accurately the level attainedby the student, using the best-fit model. A best-fit approach means that compensation should bemade when a piece of work matches different aspects of a criterion at different levels. The markawarded should be one that most fairly reflects the balance of achievement against the criterion. It isnot necessary for every single aspect of a level descriptor to be met for that mark to be awarded.

• When assessing a student’s work, teachers should read the level descriptors for each criterion untilthey reach a descriptor that most appropriately describes the level of the work being assessed. If apiece of work seems to fall between two descriptors, both descriptors should be read again and theone that more appropriately describes the student’s work should be chosen.

• Where there are two or more marks available within a level, teachers should award the upper marksif the student’s work demonstrates the qualities described to a great extent; the work may be closeto achieving marks in the level above. Teachers should award the lower marks if the student’s workdemonstrates the qualities described to a lesser extent; the work may be close to achieving marks inthe level below.

• Only whole numbers should be recorded; partial marks (fractions and decimals) are not acceptable.

• Teachers should not think in terms of a pass or fail boundary, but should concentrate on identifyingthe appropriate descriptor for each assessment criterion.

14

Internal assessment

• The highest level descriptors do not imply faultless performance but should be achievable by astudent. Teachers should not hesitate to use the extremes if they are appropriate descriptions of thework being assessed.

• A student who attains a high achievement level in relation to one criterion will not necessarilyattain high achievement levels in relation to the other criteria. Similarly, a student who attains a lowachievement level for one criterion will not necessarily attain low achievement levels for the othercriteria. Teachers should not assume that the overall assessment of the students will produce anyparticular distribution of marks.

• It is recommended that the assessment criteria be made available to students.

Practical work and internal assessment

General introductionThe internal assessment requirements are the same for biology, chemistry and physics. The internal assessment, worth 20% of the final assessment, consists of one scientific investigation. The individual investigation should cover a topic that is commensurate with the level of the course of study.

Student work is internally assessed by the teacher and externally moderated by the IB. The performance in internal assessment at both SL and HL is marked against common assessment criteria, with a total mark out of 24.

Note: Any investigation that is to be used to assess students should be specifically designed to match the assessment criteria.

The internal assessment task will be one scientific investigation taking about 10 hours and the write-up should be about 6 to 12 pages long. Investigations exceeding this length will be penalized in the communication criterion as lacking in conciseness.

The practical investigation, with generic criteria, will allow a wide range of practical activities satisfying the varying needs of biology, chemistry and physics. The investigation addresses many of the learner profile attributes well. See section on “Approaches to the teaching of chemistry” for further links.

The task produced should be complex and commensurate with the level of the course. It should require a purposeful research question and the scientific rationale for it. The marked exemplar material in the teacher support materials will demonstrate that the assessment will be rigorous and of the same standard as the assessment in the previous courses.

Some of the possible tasks include:

• a hands-on laboratory investigation

• using a spreadsheet for analysis and modelling

• extracting data from a database and analysing it graphically

• producing a hybrid of spreadsheet/database work with a traditional hands-on investigation

• using a simulation provided it is interactive and open-ended.

Some tasks may consist of relevant and appropriate qualitative work combined with quantitative work.

15

Internal assessment

The tasks include the traditional hands-on practical investigations as in the previous course. The depth of treatment required for hands-on practical investigations is unchanged from the previous internal assessment and will be shown in detail in the teacher support materials. In addition, detailed assessment of specific aspects of hands-on practical work will be assessed in the written papers as detailed in the relevant topic(s) in the “Syllabus content” section of the guide.

The task will have the same assessment criteria for SL and HL. The five assessment criteria are personal engagement, exploration, analysis, evaluation and communication.

Internal assessment details

Internal assessment componentDuration: 10 hoursWeighting: 20%• Individual investigation

• This investigation covers assessment objectives 1, 2, 3 and 4.

Internal assessment criteriaThe new assessment model uses five criteria to assess the final report of the individual investigation with the following raw marks and weightings assigned:

Personal engagement

Exploration Analysis Evaluation Communication Total

2 (8%) 6 (25%) 6 (25%) 6 (25%) 4 (17%) 24 (100%)

Levels of performance are described using multiple indicators per level. In many cases the indicators occur together in a specific level, but not always. Also, not all indicators are always present. This means that a candidate can demonstrate performances that fit into different levels. To accommodate this, the IB assessment models use markbands and advise examiners and teachers to use a best-fit approach in deciding the appropriate mark for a particular criterion.

Teachers should read the guidance on using markbands shown above in the section called “Using assessment criteria for internal assessment” before starting to mark. It is also essential to be fully acquainted with the marking of the exemplars in the teacher support material. The precise meaning of the command terms used in the criteria can be found in the glossary of the subject guides.

Personal engagementThis criterion assesses the extent to which the student engages with the exploration and makes it their own. Personal engagement may be recognized in different attributes and skills. These could include addressing personal interests or showing evidence of independent thinking, creativity or initiative in the designing, implementation or presentation of the investigation.

16

Internal assessment

Mark Descriptor

0 The student’s report does not reach a standard described by the descriptors below.

1 The evidence of personal engagement with the exploration is limited with little independent thinking, initiative or creativity.

The justification given for choosing the research question and/or the topic under investigation does not demonstrate personal significance, interest or curiosity.

There is little evidence of personal input and initiative in the designing, implementation or presentation of the investigation.

2 The evidence of personal engagement with the exploration is clear with significant independent thinking, initiative or creativity.

The justification given for choosing the research question and/or the topic under investigation demonstrates personal significance, interest or curiosity.

There is evidence of personal input and initiative in the designing, implementation or presentation of the investigation.

ExplorationThis criterion assesses the extent to which the student establishes the scientific context for the work, states a clear and focused research question and uses concepts and techniques appropriate to the Diploma Programme level. Where appropriate, this criterion also assesses awareness of safety, environmental, and ethical considerations.

Mark Descriptor


1–2 The topic of the investigation is identified and a research question of some relevance is stated but it is not focused.

The background information provided for the investigation is superficial or of limited relevance and does not aid the understanding of the context of the investigation.

The methodology of the investigation is only appropriate to address the research question to a very limited extent since it takes into consideration few of the significant factors that may influence the relevance, reliability and sufficiency of the collected data.

The report shows evidence of limited awareness of the significant safety, ethical or environmental issues that are relevant to the methodology of the investigation*.

3–4 The topic of the investigation is identified and a relevant but not fully focused research question is described.

The background information provided for the investigation is mainly appropriate and relevant and aids the understanding of the context of the investigation.

The methodology of the investigation is mainly appropriate to address the research question but has limitations since it takes into consideration only some of the significant factors that may influence the relevance, reliability and sufficiency of the collected data.

The report shows evidence of some awareness of the significant safety, ethical or environmental issues that are relevant to the methodology of the investigation.*

17

Internal assessment

Mark Descriptor

5–6 The topic of the investigation is identified and a relevant and fully focused research question is clearly described.

The background information provided for the investigation is entirely appropriate and relevant and enhances the understanding of the context of the investigation.

The methodology of the investigation is highly appropriate to address the research question because it takes into consideration all, or nearly all, of the significant factors that may influence the relevance, reliability and sufficiency of the collected data.

The report shows evidence of full awareness of the significant safety, ethical or environmental issues that are relevant to the methodology of the investigation.*

* This indicator should only be applied when appropriate to the investigation. See exemplars in TSM.

AnalysisThis criterion assesses the extent to which the student’s report provides evidence that the student has selected, recorded, processed and interpreted the data in ways that are relevant to the research question and can support a conclusion.

Mark Descriptor


1–2 The report includes insufficient relevant raw data to support a valid conclusion to the research question.

Some basic data processing is carried out but is either too inaccurate or too insufficient to lead to a valid conclusion.

The report shows evidence of little consideration of the impact of measurement uncertainty on the analysis.

The processed data is incorrectly or insufficiently interpreted so that the conclusion is invalid or very incomplete.

3–4 The report includes relevant but incomplete quantitative and qualitative raw data that could support a simple or partially valid conclusion to the research question.

Appropriate and sufficient data processing is carried out that could lead to a broadly valid conclusion but there are significant inaccuracies and inconsistencies in the processing.

The report shows evidence of some consideration of the impact of measurement uncertainty on the analysis.

The processed data is interpreted so that a broadly valid but incomplete or limited conclusion to the research question can be deduced.

5–6 The report includes sufficient relevant quantitative and qualitative raw data that could support a detailed and valid conclusion to the research question.

Appropriate and sufficient data processing is carried out with the accuracy required to enable a conclusion to the research question to be drawn that is fully consistent with the experimental data.

The report shows evidence of full and appropriate consideration of the impact of measurement uncertainty on the analysis.

The processed data is correctly interpreted so that a completely valid and detailed conclusion to the research question can be deduced.

18

Internal assessment

EvaluationThis criterion assesses the extent to which the student’s report provides evidence of evaluation of the investigation and the results with regard to the research question and the accepted scientific context.

Mark Descriptor


1–2 A conclusion is outlined which is not relevant to the research question or is not supported by the data presented.

The conclusion makes superficial comparison to the accepted scientific context.

Strengths and weaknesses of the investigation, such as limitations of the data and sources of error, are outlined but are restricted to an account of the practical or procedural issues faced.

The student has outlined very few realistic and relevant suggestions for the improvement and extension of the investigation.

3–4 A conclusion is described which is relevant to the research question and supported by the data presented.

A conclusion is described which makes some relevant comparison to the accepted scientific context.

Strengths and weaknesses of the investigation, such as limitations of the data and sources of error, are described and provide evidence of some awareness of the methodological issues* involved in establishing the conclusion.

The student has described some realistic and relevant suggestions for the improvement and extension of the investigation.

5–6 A detailed conclusion is described and justified which is entirely relevant to the research question and fully supported by the data presented.

A conclusion is correctly described and justified through relevant comparison to the accepted scientific context.

Strengths and weaknesses of the investigation, such as limitations of the data and sources of error, are discussed and provide evidence of a clear understanding of the methodological issues* involved in establishing the conclusion.

The student has discussed realistic and relevant suggestions for the improvement and extension of the investigation.

*See exemplars in TSM for clarification.

19

Internal assessment

CommunicationThis criterion assesses whether the investigation is presented and reported in a way that supports effective communication of the focus, process and outcomes.

Mark Descriptor


1–2 The presentation of the investigation is unclear, making it difficult to understand the focus, process and outcomes.

The report is not well structured and is unclear: the necessary information on focus, process and outcomes is missing or is presented in an incoherent or disorganized way.

The understanding of the focus, process and outcomes of the investigation is obscured by the presence of inappropriate or irrelevant information.

There are many errors in the use of subject specific terminology and conventions*.

3–4 The presentation of the investigation is clear. Any errors do not hamper understanding of the focus, process and outcomes.

The report is well structured and clear: the necessary information on focus, process and outcomes is present and presented in a coherent way.

The report is relevant and concise thereby facilitating a ready understanding of the focus, process and outcomes of the investigation.

The use of subject specific terminology and conventions is appropriate and correct. Any errors do not hamper understanding.

*For example, incorrect/missing labelling of graphs, tables, images; use of units, decimal places. For issues of referencing and citations refer to the “Academic honesty” section.

Rationale for practical workAlthough the requirements for IA are centred on the investigation, the different types of practical activities that a student may engage in serve other purposes, including:

• illustrating, teaching and reinforcing theoretical concepts

• developing an appreciation of the essential hands-on nature of much scientific work

• developing an appreciation of scientists’ use of secondary data from databases

• developing an appreciation of scientists’ use of modelling

• developing an appreciation of the benefits and limitations of scientific methodology.

Practical scheme of workThe practical scheme of work (PSOW) is the practical course planned by the teacher and acts as a summary of all the investigative activities carried out by a student. Students at SL and HL in the same subject may carry out some of the same investigations.

20

Internal assessment

Syllabus coverageThe range of practical work carried out should reflect the breadth and depth of the subject syllabus at each level, but it is not necessary to carry out an investigation for every syllabus topic. However, all students must participate in the group 4 project and the IA investigation.

Planning your practical scheme of workTeachers are free to formulate their own practical schemes of work by choosing practical activities according to the requirements outlined. Their choices should be based on:

• subjects, levels and options taught

• the needs of their students

• available resources

• teaching styles.

Each scheme must include some complex experiments that make greater conceptual demands on students. A scheme made up entirely of simple experiments, such as ticking boxes or exercises involving filling in tables, will not provide an adequate range of experience for students.

Teachers are encouraged to use the online curriculum centre (OCC) to share ideas about possible practical activities by joining in the discussion forums and adding resources in the subject home pages.

FlexibilityThe practical programme is flexible enough to allow a wide variety of practical activities to be carried out. These could include:

• short labs or projects extending over several weeks

• computer simulations

• using databases for secondary data

• developing and using models

• data-gathering exercises such as questionnaires, user trials and surveys

• data-analysis exercises

• fieldwork.

Practical work documentationDetails of the practical scheme of work are recorded on Form 4/PSOW provided in the Handbook of procedures. A copy of the class 4/PSOW form must be included with any sample set sent for moderation.

Time allocation for practical workThe recommended teaching times for all Diploma Programme courses are 150 hours at SL and 240 hours at HL. Students at SL are required to spend 40 hours, and students at HL 60 hours, on practical activities (excluding time spent writing up work). These times include 10 hours for the group 4 project and 10 hours for the internal assessment investigation. (Only 2–3 hours of investigative work can be carried out after the deadline for submitting work to the moderator and still be counted in the total number of hours for the practical scheme of work.)

21

Assessment

The group 4 project

The group 4 project is an interdisciplinary activity in which all Diploma Programme science students must participate. The intention is that students from the different group 4 subjects analyse a common topic or problem. The exercise should be a collaborative experience where the emphasis is on the processes involved in, rather than the products of, such an activity.

In most cases students in a school would be involved in the investigation of the same topic. Where there are large numbers of students, it is possible to divide them into several smaller groups containing representatives from each of the science subjects. Each group may investigate the same topic or different topics—that is, there may be several group 4 projects in the same school.

Students studying environmental systems and societies are not required to undertake the group 4 project.

Summary of the group 4 projectThe group 4 project is a collaborative activity where students from different group 4 subjects work together on a scientific or technological topic, allowing for concepts and perceptions from across the disciplines to be shared in line with aim 10—that is, to “develop an understanding of the relationships between scientific disciplines and their influence on other areas of knowledge”. The project can be practically or theoretically based. Collaboration between schools in different regions is encouraged.

The group 4 project allows students to appreciate the environmental, social and ethical implications of science and technology. It may also allow them to understand the limitations of scientific study, for example, the shortage of appropriate data and/or the lack of resources. The emphasis is on interdisciplinary cooperation and the processes involved in scientific investigation, rather than the products of such investigation.

The choice of scientific or technological topic is open but the project should clearly address aims 7, 8 and 10 of the group 4 subject guides.

Ideally, the project should involve students collaborating with those from other group 4 subjects at all stages. To this end, it is not necessary for the topic chosen to have clearly identifiable separate subject components. However, for logistical reasons, some schools may prefer a separate subject “action” phase (see the following “Project stages” section).

Project stagesThe 10 hours allocated to the group 4 project, which are part of the teaching time set aside for developing the practical scheme of work, can be divided into three stages: planning, action and evaluation.

PlanningThis stage is crucial to the whole exercise and should last about two hours.

• The planning stage could consist of a single session, or two or three shorter ones.

• This stage must involve all group 4 students meeting to “brainstorm” and discuss the central topic,sharing ideas and information.

22

The group 4 project

• The topic can be chosen by the students themselves or selected by the teachers.

• Where large numbers of students are involved, it may be advisable to have more than one mixedsubject group.

After selecting a topic or issue, the activities to be carried out must be clearly defined before moving from the planning stage to the action and evaluation stages.

A possible strategy is that students define specific tasks for themselves, either individually or as members of groups, and investigate various aspects of the chosen topic. At this stage, if the project is to be experimentally based, apparatus should be specified so that there is no delay in carrying out the action stage. Contact with other schools, if a joint venture has been agreed, is an important consideration at this time.

ActionThis stage should last around six hours and may be carried out over one or two weeks in normal scheduled class time. Alternatively, a whole day could be set aside if, for example, the project involves fieldwork.

• Students should investigate the topic in mixed-subject groups or single subject groups.

• There should be collaboration during the action stage; findings of investigations should be sharedwith other students within the mixed/single-subject group. During this stage, in any practically basedactivity, it is important to pay attention to safety, ethical and environmental considerations.

Note: Students studying two group 4 subjects are not required to do two separate action phases.

EvaluationThe emphasis during this stage, for which two hours are probably necessary, is on students sharing their findings, both successes and failures, with other students. How this is achieved can be decided by the teachers, the students or jointly.

• One solution is to devote a morning, afternoon or evening to a symposium where all the students, asindividuals or as groups, give brief presentations.

• Alternatively, the presentation could be more informal and take the form of a science fair wherestudents circulate around displays summarizing the activities of each group.

The symposium or science fair could also be attended by parents, members of the school board and the press. This would be especially pertinent if some issue of local importance has been researched. Some of the findings might influence the way the school interacts with its environment or local community.

Addressing aims 7 and 8Aim 7: “develop and apply 21st century communication skills in the study of science.”

Aim 7 may be partly addressed at the planning stage by using electronic communication within and between schools. It may be that technology (for example, data logging, spreadsheets, databases and so on) will be used in the action phase and certainly in the presentation/evaluation stage (for example, use of digital images, presentation software, websites, digital video and so on).

Aim 8: “become critically aware, as global citizens, of the ethical implications of using science and technology.”

23

The group 4 project

Addressing the international dimensionThere are also possibilities in the choice of topic to illustrate the international nature of the scientific endeavour and the increasing cooperation required to tackle global issues involving science and technology. An alternative way to bring an international dimension to the project is to collaborate with a school in another region.

Types of projectWhile addressing aims 7, 8 and 10 the project must be based on science or its applications. The project may have a hands-on practical action phase or one involving purely theoretical aspects. It could be undertaken in a wide range of ways:

• designing and carrying out a laboratory investigation or fieldwork.

• carrying out a comparative study (experimental or otherwise) in collaboration with another school.

• collating, manipulating and analysing data from other sources, such as scientif ic journals,environmental organizations, science and technology industries and government reports.

• designing and using a model or simulation.

• contributing to a long-term project organized by the school.

Logistical strategiesThe logistical organization of the group 4 project is often a challenge to schools. The following models illustrate possible ways in which the project may be implemented.

Models A, B and C apply within a single school, and model D relates to a project involving collaboration between schools.

Model A: mixed-subject groups and one topicSchools may adopt mixed-subject groups and choose one common topic. The number of groups will depend on the number of students.

Model B: mixed-subject groups adopting more than one topicSchools with large numbers of students may choose to do more than one topic.

Model C: single-subject groupsFor logistical reasons some schools may opt for single-subject groups, with one or more topics in the action phase. This model is less desirable as it does not show the mixed subject collaboration in which many scientists are involved.

Model D: collaboration with another schoolThe collaborative model is open to any school. To this end, the IB provides an electronic collaboration board on the OCC where schools can post their project ideas and invite collaboration from other schools. This could range from merely sharing evaluations for a common topic to a full-scale collaborative venture at all stages.

24

The group 4 project

For schools with few Diploma Programme (course) students it is possible to work with non-Diploma Programme or non-group 4 students or undertake the project once every two years. However, these schools are encouraged to collaborate with another school. This strategy is also recommended for individual students who may not have participated in the project, for example, through illness or because they have transferred to a new school where the project has already taken place.

TimingThe 10 hours that the IB recommends be allocated to the project may be spread over a number of weeks. The distribution of these hours needs to be taken into account when selecting the optimum time to carry out the project. However, it is possible for a group to dedicate a period of time exclusively to project work if all/most other schoolwork is suspended.

Year 1In the first year, students’ experience and skills may be limited and it would be inadvisable to start the project too soon in the course. However, doing the project in the final part of the first year may have the advantage of reducing pressure on students later on. This strategy provides time for solving unexpected problems.

Year 1–Year 2The planning stage could start, the topic could be decided upon, and provisional discussion in individual subjects could take place at the end of the first year. Students could then use the vacation time to think about how they are going to tackle the project and would be ready to start work early in the second year.

Year 2Delaying the start of the project until some point in the second year, particularly if left too late, increases pressure on students in many ways: the schedule for finishing the work is much tighter than for the other options; the illness of any student or unexpected problems will present extra difficulties. Nevertheless, this choice does mean students know one another and their teachers by this time, have probably become accustomed to working in a team and will be more experienced in the relevant fields than in the first year.

Combined SL and HLWhere circumstances dictate that the project is only carried out every two years, HL beginners and more experienced SL students can be combined.

Selecting a topicStudents may choose the topic or propose possible topics and the teacher then decides which one is the most viable based on resources, staff availability and so on. Alternatively, the teacher selects the topic or proposes several topics from which students make a choice.

25

The group 4 project

Student selectionStudents are likely to display more enthusiasm and feel a greater sense of ownership for a topic that they have chosen themselves. A possible strategy for student selection of a topic, which also includes part of the planning stage, is outlined here. At this point, subject teachers may provide advice on the viability of proposed topics.

• Identify possible topics by using a questionnaire or a survey of students.

• Conduct an initial “brainstorming” session of potential topics or issues.

• Discuss, briefly, two or three topics that seem interesting.

• Select one topic by consensus.

• Students make a list of potential investigations that could be carried out. All students then discussissues such as possible overlap and collaborative investigations.

A reflective statement written by each student on their involvement in the group 4 project must be included on the coversheet for each internal assessment investigation. See Handbook of procedures for more details.

26

SAMPLE QUESTION PAPERS

CHEMISTRY HL

Paper 1Paper 2Paper 3

CHEMISTRY SL

Paper 1Paper 2Paper 3

27

CHEMISTRYHIgHER lEvElPaPER 1

INSTRUCTIONS TO CANDIDATES

• Do not open this examination paper until instructed to do so.• Answer all the questions.• For each question, choose the answer you consider to be the best and indicate your choice on

the answer sheet provided.• The periodic table is provided for reference on page 2 of this examination paper.• The maximum mark for this examination paper is [40 marks].

1 hour

28

88 Ra

(226

)

56 Ba13

7.34

38 Sr87

.62

20 Ca

40.0

8

12 Mg

24.3

1

4 Be 9.012

‡†

89 ‡

Ac

(227

)

57 †

La13

8.91

39 Y88

.91

21 Sc 44.9

6

90 Th23

2.04

58 Ce

140.

12

72 Hf

178.

49

40 Zr 91.2

2

22 Ti47

.90

91 Pa23

1.04

59 Pr14

0.91

73 Ta18

0.95

41 Nb

92.9

1

23 V50

.94

92 U23

8.03

60 Nd

144.

24

74 W18

3.85

42 Mo

95.9

4

24 Cr

52.0

0

55 Cs

132.

91

37 Rb

85.4

7

19 K39

.10

11 Na

22.9

9

3 Li 6.941 H 1.011 Fr87 (223

)

Ato

mic

num

ber

Elem

ent

Rela

tive

atom

ic m

ass

93 Np

(237

)

61 Pm14

6.92

75 Re

186.

21

43 Tc 98.9

1

25 Mn

54.9

4

94 Pu (242

)

62 Sm15

0.35

76 Os

190.

21

44 Ru

101.

07

26 Fe 55.8

5

95 Am

(243

)

63 Eu15

1.96

77 Ir19

2.22

45 Rh

102.

91

27 Co

58.9

3

96 Cm

(247

)

64 Gd

157.

25

78 Pt19

5.09

46 Pd10

6.42

28 Ni

58.7

1

97 Bk (247

)

65 Tb15

8.92

79 Au

196.

97

47 Ag

107.

87

29 Cu

63.5

5

The

Peri

odic

Tab

le

98 Cf

(251

)

66 Dy

162.

50

80 Hg

200.

59

48 Cd

112.

40

30 Zn 65.3

7

99 Es (254

)

67 Ho

164.

93

81 Tl20

4.37

49 In11

4.82

31 Ga

69.7

2

13 Al

26.9

8

5 B10

.81

3

100

Fm (257

)

68 Er16

7.26

82 Pb20

7.19

50 Sn11

8.69

32 Ge

72.5

9

14 Si28

.09

6 C12

.01

4

101

Md

(258

)

69 Tm16

8.93

83 Bi20

8.98

51 Sb12

1.75

33 As

74.9

2

15 P30

.97

7 N14

.01

5

102

No

(259

)

70 Yb

173.

04

84 Po (210

)

52 Te12

7.60

34 Se78

.96

16 S32

.06

8 O16

.00

6

103

Lr (260

)

71 Lu17

4.97

85 At

(210

)

53 I12

6.90

35 Br 79.9

0

17 Cl

35.4

5

9 F19

.00

7

86 Rn

(222

)

54 Xe

131.

30

36 Kr

83.8

0

18 Ar

39.9

5

10 Ne

20.1

8

2 He

4.000

29

1. Howmanyatomsofhydrogenarein0.500molofCH3OHmolecules?

A. 231.20 10×

B. 233.01 10×

C. 236.02 10×

D. 241.20 10×

2. Calciumcarbonatereactswithhydrochloricacidaccordingtothefollowingequation.

3 2 2 2CaCO (s) 2HCl(aq) CaCl (aq) CO (g) H O(l)+ → + +

Whatisthetheoreticalyield,inmol,ofcalciumchlorideif0.10molCaCO3isaddedto100cm3of

1.0moldm–3HCl?

A. 0.050

B. 0.10

C. 0.20

D. 0.50

3. Afixedmassofanidealgasat27.0 C° and 51.01 10× Pahasavolumeof100cm3. Whichchangedoublesthevolumeofthegas?

A. Heatingthegasatconstantpressureto54.0 C° .

B. Heatingthegasatconstantpressureto327 C° .

C. Increasingthepressureonthegasto 52.02 10× Paatconstanttemperature.

D. Heatingthegasto54.0 C° andincreasingthepressureto 52.02 10× Pa.

30

4. Whichisotopehasanatomicnumberof9andamassnumberof19?

A. 9F

B. 19K

C. 19F

D. 28Si

5. Whatistheorderinwhichtheenergysub-levelsareoccupiedaccordingtotheAufbauprinciple?

A. 5s,5p,4d

B. 4d,5s,5p

C. 5s,4d,5p

D. 5s,5d,5p

6. Whichspeciesareintheorderofincreasingionicradius?

A. Cl–<K+<S2–

B. K+<Cl–<S2–

C. Cl–<S2–<K+

D. S2–<Cl–<K+

7. Whichcombinationofdescriptionsiscorrectfortheoxidesofperiod3elements?

Chlorine Magnesium Silicon Sodium

A. basic acidic basic acidic

B. acidic basic basic basic

C. basic acidic acidic acidic

D. acidic basic acidic basic

31

8. WhataretheelectronconfigurationsofCu,Cu+andCu2+?

Cu Cu+ Cu2+

A. [Ar]4s2 3d9 [Ar]4s2 3d8 [Ar]4s2 3d7

B. [Ar]4s2 3d9 [Ar]4s1 3d9 [Ar] 3d9

C. [Ar]4s2 3d9 [Ar] 3d10 [Ar] 3d9

D. [Ar]4s1 3d10 [Ar] 3d10 [Ar] 3d9

9. WhatisthecorrectnumberofcentresofnegativechargeforcarbonandtheshapeofH2CO?

C

H

OH

Centres of negative charge on C-atom Shape

A. 3 trigonalpyramidal

B. 3 trigonalplanar

C. 4 trigonalpyramidal

D. 4 trigonalplanar

10. Whichstatementaboutintermolecularforcesiscorrect?

A. The intermolecular force between H2 molecules is hydrogen bonding, because H2 hastemporarydipoles.

B. TheintermolecularforcesbetweenPH3moleculesaregreater than the intermolecularforcesbetweenNH3molecules,becausetheyhaveagreatermass.

C. TheintermolecularforcebetweenH2moleculesishydrogenbonding,becauseH2haspermanentdipoles.

D. The intermolecular forces between Br2 molecules are van der Waals’, because Br2 has temporarydipoles.

32

11. Whichsubstancesaresolubleinhexane,C6H14?

I. C8H18

II. CH4

III. H2O

A. IandIIonly

B. IandIIIonly

C. IIandIIIonly

D. I,IIandIII

12. DiagramsIandIIshowtwoporbitalsonadjacentatomsindifferentrelativeorientations.

I II

Whichtypesofbondsareformedwhentheorbitalsoverlap?

Orientation I Orientation II

A. σ σ

B. π π

C. π σ

D. σ π

33

13. Whichmoleculeshavedelocalizedπelectrons?

I. C6H6

II. CH3COOH

III. O3

A. IandIIonly

B. IandIIIonly

C. IIandIIIonly

D. I,IIandIII

14. Whataretheunitsforspecificheatcapacity?

A. kJkgK

B. kJkgK–1

C. kJkg–1K

D. kJkg–1K–1

34

15. Ineachoftwodifferentexperiments,AandB,asolutionofsodiumhydroxideisaddedtoasolutionofhydrochloricacid.Theinitialtemperatureofeachsolutionis25 C° .

ExperimentA ExperimentB

Whichstatementiscorrect?

A. ThehighestrecordedtemperatureofexperimentAislowerthanthehighestrecordedtemperatureofexperimentB.

B. Thehighestrecordedtemperatureofbothexperimentsisequal.

C. TheheatproducedinexperimentAislowerthantheheatproducedinexperimentB.

D. Theheatproducedinbothexperimentsisequal.

50cm3

1.0moldm–3NaOH(aq)50cm3

1.0moldm–3NaOH(aq)

50cm3

1.0moldm–3HCl(aq)100cm3

1.0moldm–3HCl(aq)

35

16. ThediagramrepresentstheBorn–Habercycleforthelatticeenthalpyofsodiumchloride.

WhatisthenameoftheenthalpychangesI,IIandIII?

I II III

A. ionizationenergyofNa electronaffinityofCl latticeenthalpyofNaCl

B. latticeenthalpyofNaCl ionizationenergyofNa electronaffinityofCl

C. electronaffinityofCl ionizationenergyofNa latticeenthalpyofNaCl

D. ionizationenergyofNa latticeenthalpyofNaCl electronaffinityofCl

17. Whichstatementsaboutentropyforthefollowingreactionat298Karecorrect?

2 22NO(g) O (g) 2NO (g)+ →

I. 2(O ) 0S =Ö

II. 2 22 (NO ) 2 (NO) (O )S S S S= − −Ö Ö Ö Öë

III. < 0S Öë

A. IandIIonly

B. IandIIIonly

C. IIandIIIonly

D. I,IIandIII

III

III

Na (g) Cl (g)+

122Na (g) Cl (g)+

122Na (s) Cl (g)+

NaCl(s)

H

36

18. Whichreactionisspontaneousathightemperatures,butnotatlowtemperatures?

A. 4 2 2 2CH (g) 2O (g) CO (g) 2H O(g)+ → + 0H <ë

B. 3 2CaCO (s) CO (g) CaO(s)→ + 0H >ë

C. 2 2Fe(s) Cl (g) FeCl (s)+ → 0H <ë

D. 2 32C(s) 2H O(g) CH COOH(l)+ → 0H >ë

19. TheMaxwell–Boltzmanncurvebelowshowsthedistributionofkineticenergiesfortheparticlesinasampleofgas.

Numberofparticles

KineticEnergy

Whichistheshapeofthecurveforthesamesampleofgasatahighertemperature?Allgraphsaredrawntothesamescale.

A. Numberofparticles

B. Numberofparticles

KineticEnergy KineticEnergy

C. Numberofparticles

D. Numberofparticles


37

20. ThedecompositionofN2O5occursaccordingtothefollowingequation.

2 5 2 22N O (g) 4NO (g) O (g)→ +

ThereactionisfirstorderwithrespecttoN2O5.Whatcombinationofvariablescouldtheaxesrepresentonthegraphbelow?

y

x

x-axis y-axis

A. time [N2O5]

B. [N2O5] time

C. [N2O5] rateofreaction

D. rateofreaction [N2O5]

21. Whatistheeffectofanincreaseintemperatureontherateconstantoftheforwardreaction,k,andontheequilibriumconstant,Kc,ofanexothermicreversiblereaction?

A. kdecreases,Kcincreases

B. kincreases,Kcdecreases

C. kdecreases,Kcdecreases

D. kincreases,Kcincreases

38

22. Thegraphrepresentstheratesoftheforwardandbackwardreactionsofareversiblereaction.

Rateofreaction

Time


A. XWZrepresentstherateoftheforwardreaction.

B. AtY,therateoftheforwardandbackwardreactionsiszero.

C. BetweenWandZ,theconcentrationsofproductsandreactantsareequal.

D. BetweenYandW,theconcentrationofthereactantsincreases.

23. Aliquidanditsvapourareatequilibriuminasealedcontainer.Whichofthefollowingincreaseasthecontainerisheated?

I. Themassoftheliquid.

II. Thevapourpressureoftheliquid.

III. Therateofvaporizationoftheliquid.

A. IandIIonly

B. IandIIIonly

C. IIandIIIonly

D. I,IIandIII

X

W Z

Y

39

24. Whichareconjugateacid/basepairsaccordingtotheBrønsted–Lowrytheory?

I. NH4+/NH3

II. HCOOH/HCOO–

III. H2SO4/SO42–

A. IandIIonly

B. IandIIIonly

C. IIandIIIonly

D. I,IIandIII

25. AnaqueoussolutionXreactswithasolidY,toproduceaflammablegas.WhichofthefollowingsuggestionscouldsubstancesXandYbe?

X Y

A. nitricacid,HNO3 calciumcarbonate,CaCO3

B. sulfuricacid,H2SO4 zinc,Zn

C. hydrochloricacid,HCl copper,Cu

D. sodiumhydroxidesolution,NaOH aluminumoxide,Al2O3

26. Whichiscorrectforaweakacid,HA,withconcentration0.01moldm–3at298K?

A. [H+]< –21 10×

B. pH<2

C. [OH–]< –121 10×

D. pOH>12

40

27. WhichsalthasthelowestpHwhendissolvedinwater?

A. KNO3

B. CH3COONa

C. Na2CO3

D. [Fe(H2O)6]Cl3

28. WhichofthefollowingmixtureswouldresultinthepKaoftheacidbeingobtainedfromadirectpHmeasurementoftheresultingsolution?

A. 25cm30.1moldm–3HCland25cm30.1moldm–3NaCl

B. 25cm30.1moldm–3NaOHand25cm30.1moldm–3CH3COOH

C. 12.5cm30.1moldm–3CH3COOHand25cm30.1moldm–3NaOH

D. 12.5cm30.1moldm–3NaOHand25cm30.1moldm–3CH3COOH

41

29. Anaqueoussolutionofaweakacidcontaininganindicatoristitratedwithastrongbase,resultinginthefollowingtitrationcurve.

pH

14

12

10

8

6

4

2

0Volumeofbase

AtwhichpHdoesthebufferregionoccur?

A. Between4.5and5.5

B. Between7.5and9.5

C. At9.5

D. At12

42

30. Which species has 54 electrons and 52 protons?

A.

B.

C.

D.

31. Which salts form coloured solutions when dissolved in water?

I. FeCl3 II. NiCl2III. ZnCl2

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

32. Which combination is correct for the complex ion in [Co(NH3)4(H2O)Cl]Br?

Oxidation state of cobalt Shape of the complex ion Overall charge of the

complex ion

A. +2 Octahedral +2

B. +3 Octahedral –1

C. +2 Octahedral +1

D. +2 Tetrahedral +1

212852Te

213254 Xe

213254 Xe

212852Te

43

33. What is the molecular geometry and the Cl–I–Cl bond angle in the ICl4– ion?

A. Square planar 90

B. Square pyramidal 90

C. Tetrahedral 109

D. Trigonal pyramidal 107

34. What is the geometry of the bonds around an atom with sp2 hybridization?

A. 2 bonds at 180

B. 3 bonds at 120

C. 2 bonds at 90, 1 bond at 180

D. 4 bonds at 109

35. Which reaction has the most negative ∆Hο value?

A. LiF(s) → Li+(g) + F–(g)

B. Li+(g) + F–(g) → LiF(s)

C. NaCl(s) → Na+(g) + Cl–(g)

D. Na+(g) + Cl–(g) → NaCl(s)

44

36. Which equation represents the electron affinity of calcium?

A. Ca(g) →Ca+(g) + e–

B. Ca(g) →Ca–(g) + e–

C. Ca(g) + e– → Ca–(g)

D. Ca+(g) + e– → Ca(g)

37. Consider the reaction

2I(aq) + H2O2(aq) + 2H+(aq) I2(aq) + 2H2O(l)

In the presence of S2O32–(aq) and starch solution, the time taken for a blue colour to form

was observed at various reactant concentrations.

Experiment [I–] / mol dm–3 [H2O2] / mol dm–3 [H+] / mol dm–3 Time / s

1 0.10 0.12 0.01 25

2 0.05 0.12 0.01 50

3 0.10 0.06 0.01 100

What is the correct order with respect to I– and H2O2?

I– H2O2

A. 1 2

B.

C. 2 1

D. 2 4

21

41

45

38. The expression for the equilibrium constant for a reaction is

Kc =

At a certain temperature the values of [A], [B] and [C] are all 0.2 mol dm–3. What happens to the value of Kc when all three values are doubled to 0.4 mol dm–3?

A. It is halved.

B. It does not change.

C. It doubles.

D. It increases by a factor of four.

39. At 25°C, Ka for an acid is 1.0×10–2. What is the value of Kb for its conjugate base?

A. 1.0×102

B. 1.0×10–2

C. 1.0×1012

D. 1.0×10–12

2A

CB

The strengths of organic acids can be compared using Ka and pKa values. Which acid is the strongest?

A. Acid A pKa = 6B. C. D.

Acid B pKa = 3 Acid C Ka = 1×10–5 Acid D Ka = 1×10–4

40.

46

CHEMISTRYHIGHER lEvElPaPER 2


• Write your session number in the boxes above.• Do not open this examination paper until instructed to do so.• Answer all questions.• Write your answers in the boxes provided.• A calculator is required for this paper.• A clean copy of the Chemistry data booklet is required for this paper.• The maximum mark for this examination paper is [95 marks].

2 hours 15 minutes

Candidate session number

Examination code

–

47

Answer all questions. Write your answers in the boxes provided.

1. A student used a pH meter to measure the pH of different samples of water at 298 K.

Sample pH ± 0.1

Rain water 5.1

River water 4.4

Tap water 6.5

Bottled water 7.1

(a) Use the data in the table to identify the most acidic water sample. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(b) Calculate the percentage uncertainty in the measured pH of the rain water sample. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(c) Determine the ratio of [H+] in bottled water to that in rain water.

[H+] in bottled water__________________[H+] in rain water [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

48

(d) Determine the concentration of hydroxide ions in the sample of river water. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(e) The acidity of non-polluted rain water is caused by dissolved carbon dioxide. State an equation for the reaction of carbon dioxide with water. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

49

2. The reaction between ethene and steam is used in the industrial production of ethanol.

C2H4 (g) + H2O (g) → C2H5OH (g)

The enthalpy change of the reaction can be calculated either by using average bond enthalpies or by using standard enthalpies of formation.

(a) Determine the enthalpy change of the reaction, in kJ mol–1, using the average bond enthalpies in Table 10 of the Data Booklet. [3]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(b) (i) Definethetermstandard enthalpy change of formation. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

50

(ii) Determine the enthalpy change of the reaction, in kJ mol–1, between ethene and steam using the enthalpy change of formation values given below.

Compound ∆HfÖ/ kJ mol–1

C2H5OH (g) –235

C2H4 (g) +52

H2O (g) –242 [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(c) Comment on which of the values obtained in (a) and (b)(ii) is more accurate, giving a reason. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(d) Predictthesignoftheentropychangeofthereaction,ΔS, giving a reason. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

51

3. The vapour pressure of water changes with temperature according to the graph below.

Vapo

ur p

ress

ure

/ kPa

200

180

160

140

120

100

80

60

40

20

00 20 40 60 80 100 120

Temperature / °C

(a) A liquid boils when its vapour pressure equals atmospheric pressure. Determine the boiling point of water on a mountaintop on a day when the atmospheric pressure is 60.0 kPa. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(b) Sketch another curve on the axes above to show how the vapour pressure of a liquid that has weaker intermolecular forces than water, such as bromine, changes with temperature. [1]

52

(c) (i) Asampleofliquidbrominewasleftinaclosedconical(Erlenmeyer)flaskat298Kand allowed to reach a state of equilibrium. State an observation that indicates that equilibrium was reached. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(ii) Thetemperatureoftheclosedflaskwasincreasedandthesystemwasallowedtoreach a new equilibrium. Compare the equilibrium formed at the new temperature with the equilibrium at the original temperature on the molecular level. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

53

4. Phosphorus(V) oxide, P4O10 (M r = 283.88), reacts vigorously with water (M r = 18.02),according to the equation below.

P4O10 (s) + 6H2O (l) → 4H3PO4 (aq)

(a) A student added 5.00 g of P4O10 to 1.50 g of water. Determine the limiting reactant, showing your working. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(b) Calculate the mass of phosphoric(V) acid, H3PO4 , formed in the reaction. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(c) Phosphoric(V) acid, H3PO4 , has a pKa of 2.12 (pKa1) while phosphoric(III) acid, H3PO3 , has a pKa of 1.23 (pKa1). Identify the weaker of the two acids, giving a reason for your choice.

[1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(d) State a balanced equation for the complete reaction of solid phosphorus(V) chloride, PCl5, with water, including state symbols. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

54

5. Graphite has a layered structure of carbon atoms. A section of the structure is shown below.

Layer 1

Layer 2

Layer 3

335 pm

142 pm

(a) Identify the type of attraction represented by the dotted lines shown between the layers. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(b) Graphite is used as a lubricant. Discuss two other uses of graphite with reference to its layered structure. [4]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

55

6. The Contact process involves an exothermic reversible reaction.

2SO2 (g) + O2 (g) 2SO3 (g) Kc 1 at 200 °C and 1 atm

(a) Deduce the extent of the reaction at 200 °C and 1 atm. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(b) An engineer at a Contact process plant hypothesized that using pure oxygen, instead ofair,wouldincreasetheprofits.Commentonwhetherornotherhypothesisisvalid, giving your reasons. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

56

7. A sample of magnesium contains three isotopes: magnesium-24, magnesium-25 andmagnesium-26, with abundances of 77.44 %, 10.00 % and 12.56 % respectively.(a) (i) Calculate the relative atomic mass of this sample of magnesium correct to two

decimal places. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(ii) Predict the relative atomic radii of the three magnesium isotopes, giving your reasons. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

57

(b) A graph of the successive ionization energies of magnesium is shown below.Io

niza

tion

ener

gy /

kJ m

ol–1

200 000

160 000

120 000

80 000

40 000

00 1 2 3 4 5 6 7 8 9 10 11 12

Electron removed

(i) Explain the increase in ionization energy values from the 3rd to the 8th electrons. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(ii) Explain the sharp increase in ionization energy values between the 10th and 11th electrons. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

58

(c) (i) Magnesium reacts with oxygen to form an ionic compound, magnesium oxide. Describe how the ions are formed, and the structure and bonding in magnesium oxide. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(ii) Carbon reacts with oxygen to form a covalent compound, carbon dioxide. Describe what is meant by a covalent bond. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(iii) State why magnesium and oxygen form an ionic compound while carbon and oxygen form a covalent compound. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

59

(d) (i) Predict the type of hybridization of the carbon and oxygen atoms in CO2. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(ii) Sketch the orbitals of an oxygen atom in CO2 on the energy level diagram provided, including the electrons that occupy each orbital. [2]

Energy Energy

2p

2s

Before hybridization After hybridization

(iii) Definethetermelectronegativity. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(iv) Explain why oxygen has a larger electronegativity than carbon. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

60

(e) (i) Most indicators are weak acids. Describe qualitatively how indicators work. [2]

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(ii) Identify a suitable indicator for a titration between a weak acid and a strong base, using Table 16 of the Data Booklet. [1]

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61

(a) The oxygen, that is atmospheric oxygen that is found dissolved in water in very small concentrations. Explain, in terms of intermolecular forces, why oxygen is not very soluble in water. [2]

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(b) State the relationship between the electron arrangement of an element and its group and period in the periodic table. [2]

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(c) Transition metals and their compounds often catalyse reactions. The catalyzed decomposition of hydrogen peroxide by CuO is an example. State two other examples of catalyzed reactions giving the transition metal or its compound acting as catalyst. [2]

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(d) (i) State a chemical equation for the partial dissociation of water into ions, including state symbols. [1]

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8.

62

(ii) The dissociation of water into ions is reversible. State the expression for the ionic product constant of water. [1]

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(iii) The ionic product constant of water was measured at three different temperatures.

Temperature / K Kw

298 1.00 × 10–14

313 2.92 × 10–14

373 5.13 × 10–13

Deduce whether the ionization of water is exothermic or endothermic, giving your reason. [2]

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(iv) Use the data in part (iii) to determine the pH of water at 373 K, correct to two decimal places. [2]

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63

9. Hydrogen peroxide decomposes according to the equation below.

2H2O2 (aq) → 2H2O (l) + O2 (g)

The rate of the decomposition can be monitored by measuring the volume of oxygen gas released. The graph shows the results obtained when a solution of hydrogen peroxide decomposed in the presence of a CuO catalyst.

Volu

me

of o

xyge

n / c

m3

70

60

50

40

30

20

10

00 10 20 30 40 50 60 70 80 90 100 110 120 130

Time / s

(a) (i) Outline how the initial rate of reaction can be found from the graph. [2]

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64

(ii) Explain how and why the rate of reaction changes with time. [3]

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(b) A Maxwell–Boltzmann energy distribution curve is drawn below. Label both axes and explain, by annotating the graph, how catalysts increase the rate of reaction. [3]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

65

(c) (i) In some reactions, increasing the concentration of a reactant does not increase the rate of reaction. Describe how this may occur. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(ii) Consider the reaction

2 A + B → C + D

The reaction is first orderwith respect toA, and zero order with respect to B. Deduce the rate expression for this reaction. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(d) Sketch a graph of rate constant (k) versus temperature. [1]

T

k

66

(e) Hydrochloric acid neutralizes sodium hydroxide, forming sodium chloride and water.

NaOH (aq) + HCl (aq) → NaCl (aq) + H2O (l) ΔH À = –57.9 kJ mol–1

(i) Definestandard enthalpy change of reaction, ΔH À. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(ii) Determine the amount of energy released, in kJ, when 50.0 cm3 of 1.00 mol dm–3 sodium hydroxide solution reacts with 50.0 cm3 of 1.00 mol dm–3 hydrochloric acid solution. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

67

(iii) In an experiment, 2.50 g of solid sodium hydroxide was dissolved in 50.0 cm3 of water. The temperature rose by 13.3 °C. Calculate the standard enthalpy change, in kJ mol–1, for dissolving one mole of solid sodium hydroxide in water.

NaOH (s) → NaOH (aq) [3]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(iv) Using relevant data from previous question parts, determine ΔH À, in kJ mol–1, for the reaction of solid sodium hydroxide with hydrochloric acid.

NaOH (s) + HCl (aq) → NaCl (aq) + H2O (l) [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

68

(f) (i) Zinc is found in the d-block of the periodic table. Explain why it is not considered a transition metal. [2]

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(ii) Explain why Fe3+ is a more stable ion than Fe2+ by reference to their electron configurations. [3]

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69

CHEMISTRYHIgHER lEvElPaPER 3


• Write your session number in the boxes above.• Do not open this examination paper until instructed to do so.• Section A: answer all questions.• Section B: answer all of the questions from one of the options.• Write your answers in the boxes provided.• A calculator is required for this paper.• A clean copy of the Chemistry data booklet is required for this paper.• The maximum mark for this examination paper is [45 marks].

Option Questions

Option A — Materials 3 – 7

Option B — Biochemistry 8 – 12

Option C — Energy 13 – 16

Option D — Medicinal chemistry 17 – 21

1 hour 15 minutes


Examination code

–

70

SECTION A

All the questions are compulsory in this section.

1. The table below gives the percentage of world energy supplied from various sources, in 1900and in 1998.

Source of Energy 1900 1998

Coal 94 30

Oil 4 41

Natural gas 1.5 26

Hydro-electric and nuclear sources 0.5 3

(a) Explain the significance of the data in the table for the environment.

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(b) Discuss two advantages and two disadvantages of one of the sources of energy named in the table. (Hydro-electric and nuclear power may be considered separately.)

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71

(c) Name and evaluate one sustainable source of energy not listed above.

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(d) Explain the process by which the energy is produced by coal? What type of reaction is involved in this process in terms of energy?

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(e) Can the element present in coal exist in any other form? Give an example of the other form of this element.

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(Total 15 marks)

72

SECTION B

Answer all questions from only one option.

Option A: Materials

1. Aluminium and its alloys are widely used in industry.

(a) Aluminium metal is obtained by the electrolysis of alumina dissolved in molten cryolite.

(i) Explain the function of the molten cryolite.

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(ii) State the half-equations for the reactions that take place at each electrode.

Positive electrode (anode):

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Negative electrode (cathode):

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(b) Outline two different ways that carbon dioxide may be produced during the production of aluminium.

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(Total 6 marks)

2. Catalysts may be homogeneous or heterogeneous.

(a) Distinguish between homogeneous and heterogeneous catalysts.

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73

(b) (i) Explain how a heterogeneous catalyst may increase the rate of the reaction between carbon monoxide, CO(g), and nitrogen monoxide, NO(g).

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(ii) Outline one disadvantage of using a heterogeneous catalyst rather than a homogeneous catalyst.

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(c) Discuss two factors which need to be considered when selecting a catalyst for a particular chemical process.

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(d) (i) Identify the catalyst used in the catalytic cracking of long chain hydrocarbons and state one other condition needed.

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74

(ii) State an equation for the catalytic cracking of the straight chain hydrocarbon pentadecane, C15H32, to produce two products with similar masses.

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(Total 10 marks)

3. Liquid-crystal displays are used in digital watches, calculators and laptops.

Describe the liquid-crystal state, in terms of molecular arrangement, and explain what happensas temperature increases.

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4. Kevlar is a condensation polymer that is often used in liquid-crystal displays. A section of thepolymer is shown below.

75

(i) Describe the liquid-crystal properties of Kevlar.

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(ii) Explain the strength of Kevlar in terms of its structure and bonding.

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(iii) Explain why a bullet-proof vest made of Kevlar should be stored away from acids.

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(Total 7 marks)

5. Explain in terms of structure, why low density polymers have low melting point and areflexible whereas the high density polymers high melting point.

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(Total 4 Marks )

Option B: Biochemistry

1. Polypeptides and proteins are formed by the condensation reactions of amino acids.

(a) Give the general structural formula of a 2-amino acid.

(1)

(b) Give the structural formula of the dipeptide formed by the reaction of alanine and glycine.

State the other substance formed during this reaction.

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(c) State two functions of proteins in the body.

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(Total 5 marks)

77

2. (a) Draw the straight chain structure of glucose.

(1)

(b) The structure of α-glucose is shown below.

Outline the structural difference between α-glucose and β-glucose.

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(c) Glucose molecules can condense to form starch which can exist in two forms, amylose and amylopectin. Describe the structural differences between the two forms.

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CH OH26

C

C

C C

C

O

H H

HH

H

HO

OHOH

OH

5

4

3 2

1

78

(d) 1.00 g of sucrose, C12H22O11, was completely combusted in a food calorimeter. The heat evolved was equivalent to increasing the temperature of 631 g of water from 18.36°C to 24.58 °C. Calculate the calorific value of sucrose (in kJ mol–1) given the specific heat capacity of water in Table 2 of the Data Booklet.

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(Total 9 marks)

3. Genetic information is stored in chromosomes which contain a very long DNA sequence.

(a) (i) A nucleotide of DNA contains deoxyribose, a phosphate group and an organicbase. Outline how nucleotides are linked together to form polynucleotides.

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(ii) Describe the bonding between the two strands in the double helical structure of DNA.

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(b) Explain how the sequence of different bases in DNA is related to the genetic information carried in the chromosomes.

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(c) Describe how a DNA profile can be obtained from a sample of blood taken from a child and explain how it could be used to prove whether or not a particular adult is the child’s parent.

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...................................................................................................................................... (4)

(Total 10 marks)

4. Enzymes are important molecules in the chemistry of living organisms.

(a) State what type of molecule an enzyme is and state the function of enzymes.

.....................................................................................................................................

..................................................................................................................................... (2)

(b) Explain the shape of the following graph for a reaction involving an enzyme. (4)

Rate

0 20 40 60 Temperature / ºC

81

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

..................................................................................................................................... (Total 6 marks)

Option C: Energy.

1 a). What is knocking? (1)

…………………………………………………………………………………………….

………………………………………………………………………………………………

…………………………………………………………………………………………………

……………………………………………………………………………………………….

b). What is Octane number and on what scale it is based? (2)

…………………………………………………………………………………………………

………………………………………………………………………………………………..

………………………………………………………………………………………………..

……………………………………………………………………………………………….

…………………………………………………………………………………………………

………………………………………………………………………………………………….

c). Draw the molecular structure of Isooctane. (2)

82

d). Among the following organic compounds state of increasing Octane number and (2)

explain your choice :

i) Pentane

ii) Pentene

iii) Benzene

iv) Cyclopentane

…………………………………………………………………………………………………………………………………………..

…………………………………………………………………………………………………………………………………………

…………………………………………………………………………………………………………………………………………

2 a). What is mass defect ? (2)

b). Calculate the binding energy of helium nucleus in kilo joules/moles . (2)

3 a). How is Plutonium- 239 prepared? Give equation for its formation. (2)

b). What is nuclear fission? Give an equation to show this process. (2)

c). Compare the energies produced by nuclear fission and fusion. (1)

4. What is Trans esterification? What types of oils are produced by this process? (2)

5. Give half reaction taking place for rechargeable Nickel- Cadmium batteries while (4)

a) Charging of the battery.

b) Discharging of the battery.

6. Most cracking processes used in the oil industry use either steam or a catalyst.

(a) Distinguish between these processes in terms of temperature, type of bond fission andname of the mechanism.

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

83

...................................................................................................................................

................................................................................................................................... (3)

(b) State the name of the catalyst and the type of intermediate formed in catalytic cracking.

...................................................................................................................................

...................................................................................................................................

...................................................................................................................................

................................................................................................................................... (2) (Total 5 marks)

7. Large-scale combustion of fossil fuels has been a major source of increased levels of CO2 in theatmosphere.

(a) Describe a possible effect of higher levels of CO2 in the atmosphere.

....................................................................................................................................

.................................................................................................................................... (1)

(b) Explain how the effect in (a) is caused by the interaction between CO2 and different types of radiation in the atmosphere.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

.................................................................................................................................... (2)

(Total 3 marks)

84

Option D: Medicine and drugs

1. (a) Many drugs are taken orally. State three other ways in which drugs may be taken by apatient.

……………………………………………………………………………………….

……………………………………………………………………………………….

………………………………………………………………………………………. (2)

(b) State what is meant by the term side effect.

……………………………………………………………………………………….

………………………………………………………………………………………. (1)

(Total 3 marks)

2. (i) State what is meant by the term analgesic. Explain the difference in the mode of action ofmild and strong analgesics.

…………………………………………………………………………………………..

…………………………………………………………………………………………..

…………………………………………………………………………………………..

…………………………………………………………………………………………..

…………………………………………………………………………………………..

………………………………………………………………………………………….. (3)

(ii) State the general names of the two functional groups attached to the benzene ring in a molecule of aspirin.

………………………………………………………………………………………….. (2)

(iii) The use of aspirin can have beneficial effects for the user, but can also produce some unwanted side effects. State one beneficial effect (other than its analgesic action) and one unwanted side effect.

…………………………………………………………………………………………..

…………………………………………………………………………………………..

………………………………………………………………………………………….. (2)

(Total 7 marks)

85

3. Penicillins are molecules that can kill harmful micro-organisms. Their general structure isshown in Table 21 of the Data Booklet.

(a) State the type of micro-organism killed by penicillins and explain how they do this.

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

..................................................................................................................................... (4)

(b) Explain the effect of overprescription of penicillins.

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

..................................................................................................................................... (3)

(Total 7 marks)

4. (a) Describe the differences between bacteria and viruses, by referring to their structures andthe way they multiply.

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

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.....................................................................................................................................

86

CHEMISTRYSTandaRd lEvElPaPER 1


• Do not open this examination paper until instructed to do so.• Answer all the questions.• For each question, choose the answer you consider to be the best and indicate your choice on

the answer sheet provided.• The periodic table is provided for reference on page 2 of this examination paper.• The maximum mark for this examination paper is [30 marks].

45 minutes

87

..................................................................................................................................... (4)

(b) Outline two ways in which antiviral drugs work.

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

..................................................................................................................................... (2)

(Total 6 marks)

5. (a) State the purpose of using an antacid.

.....................................................................................................................................

..................................................................................................................................... (1)

(b) State and explain which would be more effective as an antacid, 1.0 mol of magnesium hydroxide or 1.0 mol of aluminium hydroxide. Support your answer with balanced equations.

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

..................................................................................................................................... (3)

(Total 4 marks) 6. (a) Describe the likely effect of a depressant taken in:

a moderate dose. .......................................................................................................

a high dose. ............................................................................................................... (1)

(b) Ethanol in breath can be detected using a breathalyser containing potassium dichromate(VI) crystals. Describe the colour change that occurs in a positive test and identify the species responsible for the final colour.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

.................................................................................................................................... (2)

(Total 3 marks)

88

88 Ra

(226

)

56 Ba13

7.34

38 Sr87

.62

20 Ca

40.0

8

12 Mg

24.3

1

4 Be 9.012

‡†

89 ‡

Ac

(227

)

57 †

La13

8.91

39 Y88

.91

21 Sc 44.9

6

90 Th23

2.04

58 Ce

140.

12

72 Hf

178.

49

40 Zr 91.2

2

22 Ti47

.90

91 Pa23

1.04

59 Pr14

0.91

73 Ta18

0.95

41 Nb

92.9

1

23 V50

.94

92 U23

8.03

60 Nd

144.

24

74 W18

3.85

42 Mo

95.9

4

24 Cr

52.0

0

55 Cs

132.

91

37 Rb

85.4

7

19 K39

.10

11 Na

22.9

9

3 Li 6.941 H 1.011 Fr87 (223

)

Ato

mic

num

ber

Elem

ent

Rela

tive

atom

ic m

ass

93 Np

(237

)

61 Pm14

6.92

75 Re

186.

21

43 Tc 98.9

1

25 Mn

54.9

4

94 Pu (242

)

62 Sm15

0.35

76 Os

190.

21

44 Ru

101.

07

26 Fe 55.8

5

95 Am

(243

)

63 Eu15

1.96

77 Ir19

2.22

45 Rh

102.

91

27 Co

58.9

3

96 Cm

(247

)

64 Gd

157.

25

78 Pt19

5.09

46 Pd10

6.42

28 Ni

58.7

1

97 Bk (247

)

65 Tb15

8.92

79 Au

196.

97

47 Ag

107.

87

29 Cu

63.5

5

The

Peri

odic

Tab

le

98 Cf

(251

)

66 Dy

162.

50

80 Hg

200.

59

48 Cd

112.

40

30 Zn 65.3

7

99 Es (254

)

67 Ho

164.

93

81 Tl20

4.37

49 In11

4.82

31 Ga

69.7

2

13 Al

26.9

8

5 B10

.81

3

100

Fm (257

)

68 Er16

7.26

82 Pb20

7.19

50 Sn11

8.69

32 Ge

72.5

9

14 Si28

.09

6 C12

.01

4

101

Md

(258

)

69 Tm16

8.93

83 Bi20

8.98

51 Sb12

1.75

33 As

74.9

2

15 P30

.97

7 N14

.01

5

102

No

(259

)

70 Yb

173.

04

84 Po (210

)

52 Te12

7.60

34 Se78

.96

16 S32

.06

8 O16

.00

6

103

Lr (260

)

71 Lu17

4.97

85 At

(210

)

53 I12

6.90

35 Br 79.9

0

17 Cl

35.4

5

9 F19

.00

7

86 Rn

(222

)

54 Xe

131.

30

36 Kr

83.8

0

18 Ar

39.9

5

10 Ne

20.1

8

2 He

4.000

89

1. Howmanyatomsofhydrogenarein0.500molofCH3OHmolecules?

A. 231.20 10×

B. 233.01 10×

C. 236.02 10×

D. 241.20 10×

2. 1molofahydrocarbonwithgeneralformulaCnH2n+2reactscompletelywithoxygentoproduce4molofH2O.Whatistheamountofoxygenmolecules,inmol,thatreacts?

A. 4

B. 5

C. 6

D. 7

3. Underwhichcombinationofconditionsis1molofanidealgaspresent?

Volume Pressure Temperature

A. 22.4dm3 101Pa 273K

B. 22.4m3 101Pa 298K

C. 22.4dm3 101kPa 273K

D. 22.4m3 101kPa 298K

90

4. Afixedmassofanidealgasat27.0 C° and 51.01 10× Pahasavolumeof100cm3. Whichchangedoublesthevolumeofthegas?

A. Heatingthegasatconstantpressureto54.0 C° .

B. Heatingthegasatconstantpressureto327 C° .

C. Increasingthepressureonthegasto 52.02 10× Paatconstanttemperature.

D. Heatingthegasto54.0 C° andincreasingthepressureto 52.02 10× Pa.

5. 10cm3ofasolutionof1.0moldm–3NaOH(aq)isdilutedwithwateruntilthefinalvolumeis100cm3.Whatistheconcentration,inmoldm–3,ofthenewsolution?

A. 0.10

B. 1.0

C. 10.0

D. 0.01

6. Whichisotopehasanatomicnumberof9andamassnumberof19?

A. 9F

B. 19K

C. 19F

D. 28Si

91

7. An16Oatom,an16O+ionandan18O+ion,alltravellingatthesamevelocity,enterintothemagneticfieldofamassspectrometer.Whichisthepathofeachoftheparticles?

16O 16O+ 18O+

A. X Y Z

B. Y Z X

C. X Z Y

D. Z X Y

8. Whichsequenceofelementsisinorderofincreasingelectronegativity?

A. Li<Na<Rb

B. O<N<C

C. F<Cl<Br

D. Si<P<S

9. Whichcombinationofdescriptionsiscorrectfortheoxidesofperiod3elements?

Chlorine Magnesium Silicon Sodium

A. basic acidic basic acidic

B. acidic basic basic basic

C. basic acidic acidic acidic

D. acidic basic acidic basic

X

YZ

92

10. Whichsubstancehasthegreatestbondlengthbetweenthecarbonatoms?

A. C2H2

B. C2H4

C. C2H6

D. C2Cl4

11. Whichsubstancehasahighmeltingpointandconductselectriccurrentinthesolidstate?

A. Potassium

B. Potassiumchloride

C. Graphite

D. Silicondioxide

12. Whichstatementaboutintermolecularforcesiscorrect?

A. The intermolecular force between H2 molecules is hydrogen bonding, because H2 hastemporarydipoles.

B. TheintermolecularforcesbetweenPH3moleculesaregreater than the intermolecularforcesbetweenNH3molecules,becausetheyhaveagreatermass.

C. TheintermolecularforcebetweenH2moleculesishydrogenbonding,becauseH2haspermanentdipoles.

D. The intermolecular forces between Br2 molecules are van der Waals’, because Br2 hastemporarydipoles.

93

13. Whichsubstancesaresolubleinhexane,C6H14?

I. C8H18

II. CH4

III. H2O

A. IandIIonly

B. IandIIIonly

C. IIandIIIonly

D. I,IIandIII

14. Whataretheunitsforspecificheatcapacity?

A. kJkgK

B. kJkgK–1

C. kJkg–1K

D. kJkg–1K–1

94

15. Ineachoftwodifferentexperiments,AandB,asolutionofsodiumhydroxideisaddedtoasolutionofhydrochloricacid.Theinitialtemperatureofeachsolutionis25 C° .

ExperimentA ExperimentB


A. ThehighestrecordedtemperatureofexperimentAislowerthanthehighestrecordedtemperatureofexperimentB.

B. Thehighestrecordedtemperatureofbothexperimentsisequal.

C. TheheatproducedinexperimentAislowerthantheheatproducedinexperimentB.

D. Theheatproducedinbothexperimentsisequal.

16. Theenthalpychanges,inkJ,forthefollowingtworeactionsarexandy.

2 4 2 4 2 22N H (l) N O (l) 3N (g) 4H O(g)+ → + H x=Öë

2 4 2 2 2N H (l) O (g) N (g) 2H O(g)+ → + H y=Öë

Whatistheenthalpychange,inkJ,forthereaction?

2 4 2 2 4 2N H (l) 3O (g) N O (l) 2H O(g)+ → +

A. x–y

B. y–x

C. 3x–y

D. 3y–x

50cm3

1.0moldm–3NaOH(aq)50cm3

1.0moldm–3NaOH(aq)

50cm3

1.0moldm–3HCl(aq)100cm3

1.0moldm–3HCl(aq)

95

Turn over

17. Identicalpiecesofcalciumcarbonateareaddedtotwoseparateflaskscontainingexcess0.1moldm–3

hydrochloricacidatdifferenttemperatures.Themassesofthecontentsoftheflasksaremonitored.Whichgraphrepresentsthereactionatthehighertemperature?

A.

Masso

fcontentso

fflask/g

B.

Masso

fcontentso

fflask/g

0 2 4 6 0 2 4 6Time/min Time/min

C.

Masso

fcontentso

fflask/g

D.Masso

fcontentso

fflask/g

0 2 4 6 0 2 4 6Time/min Time/min

50454035302520151050

50454035302520151050

50454035302520151050

50454035302520151050

96

18. TheMaxwell–Boltzmanncurvebelowshowsthedistributionofkineticenergiesfortheparticlesinasampleofgas.

Numberofparticles

KineticEnergy

Whichistheshapeofthecurveforthesamesampleofgasatahighertemperature?Allgraphsaredrawntothesamescale.

A. Numberofparticles

B. Numberofparticles


C. Numberofparticles

D. Numberofparticles


97

Turn over

19. Thegraphrepresentstheratesoftheforwardandbackwardreactionsofareversiblereaction.

Rateofreaction

Time


A. XWZrepresentstherateoftheforwardreaction.

B. AtY,therateoftheforwardandbackwardreactionsiszero.

C. BetweenWandZ,theconcentrationsofproductsandreactantsareequal.

D. BetweenYandW,theconcentrationofthereactantsincreases.

20. TheproductionofsulfuricacidbytheContactprocessinvolvesthefollowingequilibrium.

12 2 32SO (g) O (g) 2SO (g) 196 kJmolH −+ = −

Öë

Whichstatementabouttheprocessiscorrect?

A. Anincreaseintemperaturewouldshifttheequilibriumtotheright.

B. Anincreaseintemperaturewouldincreasetherateofreaction.

C. Thepresenceofacatalystwouldshifttheequilibriumtotheright.

D. Anincreaseinpressurewouldshifttheequilibriumtotheleft.

X

W Z

Y

98

21. Whichareconjugateacid/basepairsaccordingtotheBrønsted–Lowrytheory?

I. NH4+/NH3

II. HCOOH/HCOO–

III. H2SO4/SO42–

A. IandIIonly

B. IandIIIonly

C. IIandIIIonly

D. I,IIandIII

22. 10cm3 ofNaOH solution is dilutedwith an equal volume ofwater. Which shows correctly thechangesintheconcentrationofhydroxideionsandthepH?

[OH–] pH

A. increases increases

B. increases decreases

C. decreases increases

D. decreases decreases

99

23. What will happen to the position of equilibrium and the value of the equilibriumconstant when the temperature is increased in the following reaction?

Br2(g) + Cl2(g) 2BrCl(g) ∆H = +14 kJ

Position of equilibrium Value of equilibrium constant

A. Shifts towards the reactants Decreases

B. Shifts towards the reactants Increases

C. Shifts towards the products Decreases

D. Shifts towards the products Increases (Total 1 mark)

24. What will happen if CO2(g) is allowed to escape from the followingreaction mixture at equilibrium?

H+(aq) + HCO3–(aq) CO2(g) + H2O(l)

A. The pH will decrease.

B. The pH will increase.

C. The pH will remain constant.

D. The pH will become zero. (Total 1 mark)

25. W h i c h on e of the following species can act as both a Brønsted-Lowry acid and

base in aqueous solution?

A. CH3COOH

B. NO3–

C. H2PO4–

D. OH–

(Total 1 mark)

100

26. Four aqueous solutions, I, II, III and IV, are listed below.

I. 0.100 mol dm–3 HCl

II.0.010 mol dm–3 HCl

III.0.100 mol dm–3 NaOH

IV.0.010 mol dm–3 NaOH

What is the correct order of increasing pH of these solutions?

A. I, II, III, IV

B. I, II, IV, III

C. II, I, III, IV

D. II, I, IV, III (Total 1 mark)

27. In general, the rate of a reaction can be increased by all of the following except

A. increasing the temperature.

B. increasing the activation energy.

C. increasing the concentration of reactants.

D. increasing the surface area of the reactants.(Total 1 mark)

101

28.The average bond enthalpies for O—O and O==O are 146 and 496 kJ mol–1respectively. What is the enthalpy change, in kJ, for the reaction below?

H—O—O—H(g) H—O—H(g) + ½O==O(g)

A. – 102

B. + 102

C. + 350

D. + 394 (Total 1 mark)

29.Which statement about bond enthalpies is correct?

A. Bond enthalpies have positive values for strong bonds and negative values for weak

bonds.

B. Bond enthalpy values are greater for ionic bonds than for covalent bonds.

C. Bond breaking is endothermic and bond making is exothermic.

D. The carbon–carbon bond enthalpy values are the same in ethane and ethene.

(Total 1 mark)

30. The standard enthalpy change of formation values of two oxides of phosphorus are:

P4(s) + 3O2(g) P4O6(s) HӨf= –1600 kJ mol–1

P4(s) + 5O2(g) P4O10(s) HӨf= –3000 kJ mol–1

What is the enthalpy change, in kJ mol–1, for the reaction below?

P4O6(s) + 2O2(g) P4O10(s)

A. +4600

B. +1400

C. –1400

D. –4600 (Total 1 mark)

102

CHEMISTRYSTandaRd lEvElPaPER 2


• Write your session number in the boxes above.• Do not open this examination paper until instructed to do so.• Answer all questions.• Write your answers in the boxes provided.• A calculator is required for this paper.• A clean copy of the Chemistry data booklet is required for this paper.• The maximum mark for this examination paper is [50 marks].

1 hour 15 minutes


Examination code

103

Answer all questions. Write your answers in the boxes provided.

1. A student used a pH meter to measure the pH of different samples of water at 298 K.

Sample pH ± 0.1

Rain water 5.1

River water 4.4

Tap water 6.5

Bottled water 7.1

(a) Use the data in the table to identify the most acidic water sample. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(b) Calculate the percentage uncertainty in the measured pH of the rain water sample. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(c) Determine the ratio of [H+] in bottled water to that in rain water.

[H+] in bottled water__________________[H+] in rain water [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

104

(d) The acidity of non-polluted rain water is caused by dissolved carbon dioxide. State an equation for the reaction of carbon dioxide with water. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

105

2. Graphite has a layered structure of carbon atoms. A section of the structure is shown below.

Layer 1

Layer 2

Layer 3

335 pm

142 pm

(a) Explain why the distance between adjacent carbon atoms within a layer is shorter than the distance between layers. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(b) Graphite is used as a lubricant. Discuss two other uses of graphite with reference to its layered structure. [3]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

106

3. The Contact process involves an exothermic reversible reaction.

2SO2 (g) + O2 (g) 2SO3 (g) Kc 1 at 200 °C and 1 atm

(a) Deduce the extent of the reaction at 200 °C and 1 atm. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(b) The Contact process operates at a temperature of 450 °C and a pressure of 2 atm as optimum conditions for the production of SO3. Outline the reasons for choosing these conditions. [4]

Temperature:

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Pressure:

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107

(c) An engineer at a Contact process plant hypothesized that using pure oxygen, instead ofair,wouldincreasetheprofits.Commentonwhetherornotherhypothesisisvalid, giving your reasons. [2]

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108

4. (a) A sample of magnesium contains three isotopes: magnesium-24, magnesium-25 andmagnesium-26, with abundances of 77.44 %, 10.00 % and 12.56 % respectively.(i) Calculate the relative atomic mass of this sample of magnesium correct to two

decimal places. [2]

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(ii) By reference to the deflection and detection stages in the mass spectrometer, explain how the mass and abundance of an isotope are determined. [2]

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(iii) Predict the relative atomic radii of the three magnesium isotopes, giving your reasons. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

109

(b) Describe the bonding in magnesium. [2]

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(c) State an equation for the reaction of magnesium oxide with water. [1]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(d) Phosphorus(V) oxide, P4O10 (M r = 283.88), reacts vigorously with water (M r = 18.02), according to the equation below.

P4O10(s) + 6H2O(l) → 4H3PO4(aq)

(i) A student added 5.00 g of P4O10 to 1.50 g of water. Determine the limiting reactant, showing your working. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(ii) Calculate the mass of phosphoric(V) acid, H3PO4 , formed in the reaction. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

110

(iii) State a balanced equation for the reaction of aqueous H3PO4 with excess aqueous sodium hydroxide, including state symbols. [2]

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(iv) State the formula of the conjugate base of H3PO4. [1]

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(e) (i) Deduce the Lewis structure of PH4+. [1]

111

(ii) Predict, giving a reason, the bond angle around the phosphorus atom in PH4+. [2]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

(iii) Predict whether or not the P–H bond is polar, giving a reason for your choice. [1]

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112

(iii) In an experiment, 2.50 g of solid sodium hydroxide was dissolved in 50.0 cm3 of water. The temperature rose by 13.3 °C. Calculate the standard enthalpy change, in kJ mol–1, for dissolving one mole of solid sodium hydroxide in water.

NaOH (s) → NaOH (aq) [3]

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(iv) Using relevant data from previous question parts, determine ΔH À, in kJ mol–1, for the reaction of solid sodium hydroxide with hydrochloric acid.

NaOH (s) + HCl (aq) → NaCl (aq) + H2O (l) [2]

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113

5. (a) State the property that determines the order in which elements are arranged in theperiodic table. [1]

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(b) State the relationship between the electron arrangement of an element and its group and period in the periodic table.

[2]

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(This question continues on the following page)

114

(a) Hydrogen peroxide decomposes according to the equation below.

2H2O2 (aq) → 2H2O (l) + O2 (g)

The rate of the decomposition can be monitored by measuring the volume of oxygen gas released. The graph shows the results obtained when a solution of hydrogen peroxide decomposed in the presence of a CuO catalyst.

Volu

me

of o

xyge

n / c

m3

70

60

50

40

30

20

10

00 10 20 30 40 50 60 70 80 90 100 110 120 130

Time / s

(i) The experiment is repeated with the same amount of a more effective catalyst, MnO2, under the same conditions and using the same concentration and volume of hydrogen peroxide. On the graph above, sketch the curve you would expect. [1]

(This question continues on the following page)

6.

115

(ii) Outline how the initial rate of reaction can be found from the graph. [2]

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(iii) Outline a different experimental procedure that can be used to monitor the decomposition rate of hydrogen peroxide. [1]

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(iv) A Maxwell–Boltzmann energy distribution curve is drawn below. Label both axes and explain, by annotating the graph, how catalysts increase the rate of reaction. [2]

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116

CHEMISTRYSTANDARD lEvElPAPER 3


• Write your session number in the boxes above.• Do not open this examination paper until instructed to do so.• Section A: answer all questions.• Section B: answer all of the questions from one of the options.• Write your answers in the boxes provided.• A calculator is required for this paper.• A clean copy of the Chemistry data booklet is required for this paper.• The maximum mark for this examination paper is [35 marks].

Option Questions

Option A — Materials 3 – 6

Option B — Biochemistry 7 – 9

Option C — Energy 10 – 12

Option D — Medicinal chemistry 13 – 15

1 hour


Examination code

–

117

SECTION : A

Answer all the questions of this section.

1. The table below gives the percentage of world energy supplied from various sources, in 1900and in 1998.

Source of Energy 1900 1998

Coal 94 30

Oil 4 41

Natural gas 1.5 26

Hydro-electric and nuclear sources 0.5 3

(a) Explain the significance of the data in the table for the environment.

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(b) Discuss two advantages and two disadvantages of one of the sources of energy named in the table. (Hydro-electric and nuclear power may be considered separately.)

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118

(c) Name and evaluate one sustainable source of energy not listed above.

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(d) Explain the process by which the energy is produced by coal? What type of reaction is involved in this process in terms of energy?

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(e) Can the element present in coal exist in any other form? Give an example of the other form of this element.

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(Total 15 marks)

119

SECTION B

Answer all the questions from any one option.

Option A: Materials

1. Aluminium and its alloys are widely used in industry.

(a) Aluminium metal is obtained by the electrolysis of alumina dissolved in molten cryolite.

(i) Explain the function of the molten cryolite.

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........................................................................................................................... (1)

(ii) State the half-equations for the reactions that take place at each electrode.

Positive electrode (anode):

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Negative electrode (cathode):

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(b) Outline two different ways that carbon dioxide may be produced during the production of aluminium.

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(Total 5 marks)

2. Catalysts may be homogeneous or heterogeneous.

(a) Distinguish between homogeneous and heterogeneous catalysts.

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(1)

120

(b) Outline one disadvantage of using a heterogeneous catalyst rather than a homogeneous catalyst.

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(c) Discuss two factors which need to be considered when selecting a catalyst for a particular chemical process.

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(d) (i) Identify the catalyst used in the catalytic cracking of long chain hydrocarbons and state one other condition needed.

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121

(ii) Why are Nanoparticles effective heterogeneous catalysts?

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(Total 8 marks)

3. Liquid-crystal displays are used in digital watches, calculators and laptops.

Describe the liquid-crystal state, in terms of molecular arrangement, and explain what happensas temperature increases.

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4. Kevlar is a condensation polymer that is often used in liquid-crystal displays. A section of thepolymer is shown below.

(i) Explain the strength of Kevlar in terms of its structure and bonding.

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122

(ii) Explain why a bullet-proof vest made of Kevlar should be stored away from acids.

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(Total 4 marks)

Option B : Biochemistry

1. The structures of the amino acids glycine and serine are shown in Table 20 of the Data Booklet.

(i) Draw the structure of one of the dipeptides formed when one molecule of glycine and onemolecule of serine react together. Show all the bonds in the link between the two molecules.

(3)

(Total 3 marks)

123

2. (a) The general formula for saturated fatty acids is CnC2nO2. The molecular formula oflinoleic acid is C18H32O2.

(i) Determine the number of carbon to carbon double bonds in linoleic acid.

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(ii) Iodine number is defined as the number of grams of iodine that adds to 100 g of a fat or an oil in an addition reaction. Determine the iodine number of linoleic acid.

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(Total 4 marks)

124

4. Identify three types of interactions responsible for the tertiary structure of proteins.

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5.

(b) What is vitamin fortification?

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(c) State the function of vitamin D in the human body and describe one effect of vitamin D deficiency.

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(Total 4 marks)

6. (a) Compare the structural properties of starch and maltose.

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(Total 3 marks)

125

7. Fats and oils are formed when fatty acids react with glycerol.

(a) Outline two structural differences between saturated and unsaturated fats.

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(b) Explain why saturated fats have higher melting points than unsaturated fats with similar relative molecular masses.

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(Total 4 marks)

Option C: Energy.

1 a). What is knocking ? (1)

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b).What is Octane number and on what scale is it based ? (1)

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c). Draw the molecular structure of Isooctane. (2)

d). Among the following organic compounds state of increasing Octane number and

explain your choice : (2)

i) Pentane

ii) Pentene

iii) Benzene

iv) Cyclopentane

…………………………………………………………………………………………………………

………………………………………………………………………………………………………...

…………………………………………………………………………………………………………

………………………………………………………………………………………………………

…………………………………………………………………………………………………………

………………………………………………………………………………………………………..

2 Calculate the binding energy of helium nucleus in kilo joules /moles . (2)

3 What is nuclear fission? Give an equation to show this process. (2)

4. What is Tran’s esterification? What types of oils are produced by this process? (2)

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5. Most cracking processes used in the oil industry use either steam or a catalyst.

(a) Distinguish between these processes in terms of temperature, type of bond fission and name of the mechanism.

...................................................................................................................................

...................................................................................................................................

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...................................................................................................................................

...................................................................................................................................

................................................................................................................................... (3)

(b) State the name of the catalyst and the type of intermediate formed in catalytic cracking.

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................................................................................................................................... (2)

(Total 5 marks)

6. Large-scale combustion of fossil fuels has been a major source of increased levels ofCO2 in the atmosphere.

(a) Describe a possible effect of higher levels of CO2 in the atmosphere.

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.................................................................................................................................... (1)

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(b) Explain how the effect in (a) is caused by the interaction between CO2 and different types of radiation in the atmosphere.

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.................................................................................................................................... (2)

(Total 3 marks)

Option D: Medicine and drugs

1. (a) Many drugs are taken orally. State three other ways in which drugs may be taken by apatient.

……………………………………………………………………………………….

……………………………………………………………………………………….

………………………………………………………………………………………. (2)

(b) State what is meant by the term side effect.

……………………………………………………………………………………….

………………………………………………………………………………………. (1)

(Total 3 marks)

2. (i) State what is meant by the term analgesic. Explain the difference in the mode of action ofmild and strong analgesics.

…………………………………………………………………………………………..

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…………………………………………………………………………………………..

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…………………………………………………………………………………………..

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………………………………………………………………………………………….. (3)

(ii) State the general names of the two functional groups attached to the benzene ring in a molecule of aspirin.

…………………………………………………………………………………………..

…………………………………………………………………………………………

…………………………………………………………………………………………. (2)

(iii) The use of aspirin can have beneficial effects for the user, but can also produce some unwanted side effects. State one beneficial effect (other than its analgesic action) and one unwanted side effect.

…………………………………………………………………………………………..

…………………………………………………………………………………………..

………………………………………………………………………………………….. (2)

(Total 7 marks)

4. (a) Describe the differences between bacteria and viruses, by referring to their structures andthe way they multiply.

.....................................................................................................................................

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(b) Outline two ways in which antiviral drugs work.

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

..................................................................................................................................... (2)

(Total 6 marks)

(c) State the purpose of using an antacid.

.....................................................................................................................................

..................................................................................................................................... (1)

(Total 1 marks)

5. (a) What is therapeutic window?

…………………………………………………………………………………………

…………………………………………………………………………………………..

………………………………………………………………………………………….

…………………………………………………………………………………………. (1)

(b) Give two reasons why HIV is proving more challenging than other viruses to defeat.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

.................................................................................................................................... (2)

(Total 3 marks)

131

EXTENDED ESSAY SAMPLE

132

EXTENDED ESSAY

What effect does the brewing time of loose tea of a variety of commercial brands (Twinnings

Earl Grey, Lipton Darjeeling Tea, Taj Mahal and Brooke Bond Red Label) have on the amount

of caffeine dissolved in the drink and the pH level of the drink?

Candidate Name: XXXX

Candidate Number: 002798XXXX

Exam Session: May 20XX

Name of School: Symbiosis International School

School Code: 002798

Word Count: 3, 990.

133

1

Table of contents.

Page Number Subtitle

3 Acknowledgments.

4 Abstract.

5 Introduction.

8 Introduction - Camellia sinensis.

10 Research Question.

10 Hypothesis.

11 Variables.

12 Apparatus.

13 Procedure.

17 Results- Twinnings Earl Grey caffeine content.

19 Results- Twinnings Earl Grey pH levels.

21 Results- Lipton Darjeeling Tea caffeine content.

23 Results- Lipton Darjeeling Tea pH levels.

25 Results- Taj Mahal caffeine content.

27 Results- Taj Mahal pH levels.

29 Results- Brooke Bond Red Label caffeine content.

31 Results- Brooke Bond Red Label pH levels.

33 Results- collective caffeine content.

35 Results- collective pH levels.

37 Qualitative analysis.

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39 Conclusion.

41 Evaluation.

45 Bibliography.

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3

Acknowledgements:

First, I would like to thank both my supervisors, Mrs. Anuradha Chaturvedi and Mrs. Amita Seth

for their generous support and continuous encouragement throughout this investigation. This

research would not have been possible without their valuable guidance. I would also like to thank

the lab assistant, Mr. Manoj for supplying me with all the necessary equipment. I wish to express

my gratitude and love to my family for their abundant love and support.

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Abstract:

Tea is a beverage drunk in mostly every household in India. Although originally created for

medicinal purposes, tea is now had for gustatory pleasure. However, most people are unaware of

the effect of brewing time on contents of caffeine present in the tea leaves and the tea’s acidity

(pH) level. Since my family consumes about three servings of tea a day, I was intrigued to find

out how much caffeine they were consuming daily and how their brewing time could lead to the

problem of acidity. The research question for my investigation is “What effect does the

brewing time of loose tea of a variety of commercial brands (Twinnings Earl Grey, Lipton

Darjeeling Tea, Taj Mahal and Brooke Bond Red Label) have on the amount of caffeine

dissolved in the drink and the pH level of the drink?”

I selected four brands, Twinnings Earl Grey, Lipton Darjeeling Tea, Taj Mahal and Brooke Bond

Red Label. I then boiled 2g of each tea with steeping times ranging from 60 seconds to 300

seconds and used chloroform as the basic solvent to extract the caffeine, along with sodium

hydroxide and distilled water. To calculate the pH I used a digital pH meter.

The results showed an increase in the mass of the caffeine extracted and a decrease in the pH

levels as the brewing time was increased. Lipton Darjeeling Tea was found to contain the most

caffeine while Twinnings Earl Grey contained the least. The most acidic tea was Taj Mahal (a

local favorite) and the least acidic was Lipton Darjeeling Tea.

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Introduction:

Tea is an aromatic beverage commonly prepared by pouring hot or boiling water over cured

leaves of the tea plant, Camellia sinensis.1 Being the most popular beverage after water, tea has a

slightly bitter and astringent taste that people all around the globe enjoy.

Although it is not confirmed, most people think that tea has originated from China, where it was

first used as a medicinal drink. Tea became a widespread beverage in Britain in the 17th century,

after which the British introduced it to the Indians to compete with the Chinese’s monopoly on

the product.

Various methods of making tea have been evolved over time and each culture has its own

preferred way. Milk was added to tea for the first time in Europe. Soon, Indians began adding

milk to their tea and this has now become the traditional way to drink this majorly loved

beverage. Masala chai is an Indian specialty which involves the addition of different spices to the

cured leaves tea leaves before they have been completely boiled.

Tea, like coffee, contains caffeine. Caffeine is a white crystalline alkaloid and a stimulant drug.

It is the reason for tea having an overly bitter taste, since it is found in the leaves of the tea plant

itself. Caffeine’s IUPAC name is 1,3,7-Trimethyl-1H-purine-2,6(3H,7H)-dione 3,7-Dihydro-

1,3,7-trimethyl-1H-purine-2,6-dione, and it’s structural formula is C8H10N4O2.

1. Thomas Fuller, "A Tea From the Jungle Enriches a Placid Village," The New York Times (New York), April 21,2008.

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Caffeine has major effects on humans, especially on our nervous systems. It acts as a central

nervous system stimulant; so it basically wards off drowsiness and resorts alertness for a period

of time. Caffeine is the world’s most widely used psychoactive drug. However unlike most other

psychoactive drugs, caffeine is legal worldwide and is unregulated in most countries.

Approximately all energy drinks contain caffeine, including coffee and tea.

The effect of caffeine on different people is variable since the amount of caffeine that triggers the

central nervous system for each person is different. For some people, a small amount of caffeine

taken during the evening hours is enough to disrupt their sleep for the night, however, for others

small amounts of caffeine are ineffective and do not disrupt sleeping patterns at all.

Caffeine has been recognized by the Food and Drug Administration as GRAS (generally

recognized as safe) because it only becomes toxic once the intake amount has crossed one gram.

For most other toxins the limit is 500 milligrams.

Consumption of large amounts of caffeine – usually more than 250 mg per day – can lead to a

condition known as caffeinism. Caffeinism usually combines caffeine dependency with a wide

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range of unpleasant physical and mental conditions including nervousness, irritability,

restlessness, insomnia, headaches, and heart palpitations after caffeine use.2

Coffee accounts for some 54 per cent of ingested caffeine, while tea accounts for some 43 per

cent.3

Considering how my parents consume tea about three to four times a day, I wondered how much

caffeine each serving contained, since sometimes my father was kept awake late at night due to

his last cup of tea. Another thing I noticed was that sometimes my parents complained about

acidity problems after drinking tea. I questioned my mother on the amount of time she brews her

tea for. Upon asking my aunt how long she brews her tea for, I realized that some people brew

their tea for a longer amount of time. I researched and found many investigations using liquid

chromatography to determine the amount of caffeine found in different cups of coffee brewed for

different amounts of times. Instead of testing coffee, however, I decided to test tea since this is

the most common beverage besides water drunk by most Indians. Since acidity also was a major

effect of the beverage, I decided to investigate this factor too.

This lead to my research question “What effect does the brewing time of loose tea of a variety

of commercial brands (Twinnings Earl Grey, Lipton Darjeeling Tea, Taj Mahal and

Brooke Bond Red Label) have on the amount of caffeine dissolved in the drink and the pH

level of the drink?”

2. Smith BD, Gupta U, and Gupta BS, Caffeine and activation theory: effects on health and behavior, (CRC Press,2007) , 331-344. 3. “What’s your poison?,” Abc, accessed September 11, 2013,www.abc.net.au/quantum/poison/caffeine/caffeine.html.

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Camellia sinensis:

It is the species of plant whose leaves and leaf buds are used to produce the tea. It belongs to the

genus Camellia, which is a genus of flowering plants in the family Theaceae. White tea, yellow

tea, green tea, oolong, pu-erh tea and black tea are all harvested from this species, but

are processed differently to attain different levels of oxidation. There are two major varieties

used for tea, Chinese tea, Camellia sinensis var. sinensis, and Assam tea, Camellia

sinensis var. assamica.4

The seeds of Camellia sinensis and Camellia oleifera can be pressed to yield tea oil. Not to

confuse it with tea tree oil which is an essential oil that is used for medical and cosmetic

purposes, and originates from the leaves of a different plant, tea oil is a sweetish seasoning and

cooking oil.

The leaves of the plant are usually 4–15 cm long and 2–5 cm broad. Fresh leaves contain about

4%caffeine.5 The young leaves are light green while the older ones are a deeper green. Besides

the color difference, older and younger leaves also have varying chemical compositions which

result in different tea qualities. Typically, only the bud and the topmost two or three leaves are

harvested for the production of tea.

Although there are a variety of different tea types, mainly three are cultivated and produced in

India. They are: Assam tea, Darjeeling tea and Nilgiri tea. Assam tea naturally comes from the

northeastern section of the country and it was first established in 1837. Darjeeling tea comes

from a cool region which is located at the foot of the Himalayas. This tea is considered to be one

4. “Camellia sinensis (L. Kuntze),” IT IS Report, accessed October 10, 2013,http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=506801. 5. “Camellia sinensis (L.) Kuntze,” Purdue, accessed October 12, 2013,http://www.hort.purdue.edu/newcrop/duke_energy/Camellia_sinensis.html.

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of the finest in the world. Nilgiri tea comes from a region higher than that of the Darjeeling and

is most delicate in flavor.

Other than naturally being found in the leaves of the Camellia sinensis, caffeine is also forcefully

localized into the vascular bundles of the plant using immunohistochemical methods. The

precursor phloem was suggested to be the main area of accumulation of caffeine. Caffeine was

also determined to be present within the precursor xylem, but in a lower concentration. It was

hypothesized that caffeine is synthesized within the chloroplasts of photosynthetic cells and

transported to the vascular bundles where it acts as a chemical defense against various pathogens

and predators. 6

6. Van Breda SV., van der Merwe CF., Robbertse H. and Apostolides Z, “Immunohistochemical localization ofcaffeine in young Camellia sinensis (L.) O. Kuntze (tea) leaves,” PubMed, accessed October 11, 2013, doi: 10.1007/s00425-012-1804-x.

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Research question:

What effect does the brewing time of loose tea of a variety of commercial brands

(Twinnings Earl Grey, Lipton Darjeeling Tea, Taj Mahal and Brooke Bond Red Label)

have on the amount of caffeine dissolved in the drink and the pH level of the drink?

Hypothesis:

I hypothesize that as the brewing time increases, the amount of caffeine dissolved in the tea will

increase. I think this way because if the brewing time is, for example, only 10 seconds, then not

much caffeine from the tea leaves will be able to leave the leaves. However, if the time frame is

longer, more caffeine can leave the leaves thus reducing the mass of caffeine found in the tea

leaves.

The pH of the drink however, will decrease as the brewing time increases, making it more acidic.

This is because (according to an investigation carried out in 2001) black tea consists of oxalates

and citrates which are acidic anions. As the tea leaves are boiled, more and more amounts of

oxalates and citrates diffuse out of the leaves and into the water, leaving the drink more acidic.7

7. “Acidity of Tea,” Rate Tea, accessed September 10, 2013, http:// ratetea.com/topic/acidity-of-tea/79/.

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Variables:

1. Independent:

The amount of time the tea is brewed for (60 seconds, 120 seconds, 180 seconds, 240

seconds and 300 seconds) and the brand of the tea.

2. Dependent:

The mass of the caffeine dissolved in the tea and the pH of the drink.

3. Controlled:

the volume of water

the pH and temperature of water

the number of trials taken for each tea brand and each time interval

the weighing scale used to weigh the masses

the measuring cylinders

the chemicals

Methods to control variables:

volume of water: by using 100ml each time from a measuring cylinder (100ml±1ml)

pH and temperature of water: by using distilled water

the chemicals: by using them from the same source each time

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Apparatus:

Name Amount/ Number Capacity Uncertainty

Bunsen Burner 5 - -

Glass beakers 15 150ml -

Spatula 2 - -

Stirring rod 1 - -

Digital thermometer 5 - ±0.01 .C

Glass trough 1 - -

Separatory funnel 1 200ml -

Digital weighing scale 1 200g ±0.001g

Measuring cylinder 5 10ml ±0.1ml

Measuring cylinder 1` 100ml ±1ml

Stopwatch 1 - ±0.01s

Glass slide 2 10ml -

Filter paper 80 - -

Chloroform 1500mL - -

Tongs 1 pair - -

Sodium hydroxide 256g - -

Distilled water 8536mL - -

pH meter. 1 14 ±0.1

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Procedure8:

Part A) Making the tea.

1. Pour out 100ml of distilled water in to a measuring cylinder (100ml±1ml)

2. Pour this 100ml of water into a 200ml beaker.

3. Place the beaker on a Bunsen burner and start the burner.

4. Put a thermometer (±0.01.C) in the beaker.

5. Place a petri dish on the digital weighing scale (±0.001g)and tare it.

6. Using a spatula, measure 2 grams of tea of one of the brands on the same digital balance.

7. Once the thermometer (±0.01.C) in the beaker reads 99.C, transfer the 2 grams of tea into

it.

8. Start the stopwatch (±0.01s) immediately and keep stirring the water.

9. When the stopwatch reads 60 seconds switch off the burner.

10. Using the hot water tongs pick up the beaker and place it on the slab.

11. Strain the tea from the beaker into another beaker using filter paper.

12. Place the beaker in to a trough containing water at room temperature (roughly around

34.C).

13. Once the 200ml beaker has reached 34.C, take it out of the trough.

14. Label it as “60s trial 1”.

15. Switch on the pH meter and place it into the drink.

16. Leave it there until the value on the screen stops fluctuating.

17. Record this reading.

8. “The Isolation of Caffeine from Tea,” Oxford, accessed August 2, 2013,http://www.oxford.net/~mavarod/portal/school/caffeine.html.

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Part B) Preparing the 6M NaOH solution.

1. Place a petri dish on a digital weighing balance (±0.001g).

2. Press the tare button so that the weight of the petri dish is taken to be 0g.

3. Using a spatula weigh out 24g of sodium hydroxide flakes.

4. Transfer this into a 200ml beaker.

5. Measure 100ml of distilled water using a measuring cylinder (100ml±1ml).

6. Pour this water into the beaker containing the flakes.

7. Using a glass stirrer, dissolve the NaOH flakes in the water by constantly stirring them.

8. Label this beaker as “NaOH solution” and keep it aside.

Part C) Extracting the caffeine.

1. Pour the contents of the beaker containing the tea into a separating funnel.

2. Allow this to settle.

3. Measure out 6.7 ml of chloroform using a measuring cylinder (10ml±0.1ml)

4. Pour this into the separating funnel.

5. Invert the separatory funnel back and forth ten times, but stop every three times to allow

the gas produced to escape. An organic layer should form.

6. Release this organic layer into a separate beaker (200ml)

7. Repeat the 6.7 ml washing with chloroform two more times, and after each one release

the organic layer into that same beaker.

8. After the three washings, discard the contents of the separating funnel and transfer the

organic content placed in the other beaker in to the separating funnel.

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9. Wash this organic content twice with 6.7ml of the 6M NaOH solution prepared earlier.

Don’t remove anything from the separating funnel.

10. Then wash the contents of the separating funnel with 6.7ml of distilled water.

11. Place a fresh beaker onto the weighing balance and record its mass.

12. Pour the contents of the separating funnel into the beaker whose mass was measured.

13. Place this beaker on to a wire gauze place on top of a tripod stand above a Bunsen burner

and wait till the liquid has evaporated. This may take some time.

14. The remaining white crystals are the caffeine.

Part D) Recording the readings.

1. Place the beaker containing the crystals on the weighing balance.

2. Record the mass

3. Subtract the mass of the beaker recorded earlier from this new mass to obtain the mass of

the caffeine.

Part E) Performing the complete experiment.

Part A to Part D of the above procedure only describes the preparation of one trial of one time

interval of one tea brand. The parts must be performed three more times using the same tea

brand’s tea for a 60 seconds brewing time. However, part B must not be repeated as many times

since in the first go 50ml is made when only 13.4 ml is used. Then the parts must be done four

times using the same brand’s loose tea for 120s brewing time, then four times for180 seconds

brewing time and so on until there are four trials for each time interval, from 60 seconds to 300

seconds. After each trial, wash and dry the beakers, measuring cylinders, spatulas, separating

funnel, glass slides and stirrers well so that none of the remnants from the previous trial are

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present during the next. Once that is done, the entire process must be repeated using another tea

brand. Then, with the third and fourth tea brand too.

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Results:

Twinnings Earl Grey.

Table 1.1: Mass of caffeine extracted from the tea in mg ± 0.1mg

Brewing time in

seconds of 2g tea in

100ml water each

Trials for caffeine mass in mg ± 0.1mg Processed Data

1 2 3 4 Average Standard

Deviation

60 15.7 16.0 16.2 15.9 15.95 0.623212

120 17.8 17.5 18.1 17.7 17.78 0.250000

180 21.0 21.8 22.0 20.9 21.43 0.556028

240 22.9 22.6 22.6 23.1 22.80 0.244949

300 29.3 29.1 28.9 30.2 29.38 0.573730

Sample calculation of mean for 60 seconds brewing time:

Average = (15.7 + 16.0 + 16.2 + 15.9) / 4 = 15.98.

(Standard deviation was calculated using a function on Microsoft excel)

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Graph 1.1: Average mass of caffeine extracted from Twinnings Earl Grey tea.

(The error bars represent standard deviation)

0

5

10

15

20

25

30

35

60 120 180 240 300Ave

rage

mas

s of

caf

fein

e ex

trac

ted

in m

g ±

0.1m

g

Brewing time in seconds ± 0.1s

Mass of caffeine extracted against brewing time.

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Table 1.2: pH levels of Twinnings Earl Grey tea.

Brewing time in


100ml water each

Trials for pH level Processed Data


Deviation

60 5.4 5.4 5.3 5.4 5.4 0.050000

120 5.0 5.1 5.0 5.0 5.0 0.050000

180 5.0 5.0 5.0 4.9 5.0 0.050000

240 4.9 5.0 5.0 4.9 5.0 0.057735

300 4.9 4.9 4.9 4.8 4.9 0.050000


Average = (5.4 + 5.4 + 5.3 + 5.4) / 4 = 5.4.


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Graph 1.2: average pH levels of Twinnings Earl Grey tea.


4.5

4.6

4.7

4.8

4.9

5

5.1

5.2

5.3

5.4

5.5

60 120 180 240 300

Ave

rage

pH

leve

l of

the

dri

nk

±0.

1


pH levels against brewing time

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Lipton Darjeeling Tea.

Table 2.1: mass of caffeine extracted in mg±0.1mg from Lipton Darjeeling Tea.

Brewing time in


100ml water each



Deviation

60 45.2 45.6 46.3 45.6 45.68 0.457347

120 54.7 55.0 54.9 54.7 54.83 0.150000

180 63.6 64.4 63.8 64.0 63.95 0.341565

240 72.3 73.4 73.1 73.1 72.98 0.471699

300 88.6 89.3 89.0 88.9 88.95 0.288675


Average = ( 45.2 + 45.6 + 46.3 + 45.6 ) / 4 = 45.68.


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Graph 2.1: Average mass of caffeine extracted in mg±0.1mg from Lipton Darjeeling Tea.


0

10

20

30

40

50

60

70

80

90

100

60 120 180 240 300

Ave

rage

mas

s of

caf

fein

e ex

trac

ted

in m

g ±

0.1m

g



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Table 2.2: pH levels for Lipton Darjeeling Tea.

Brewing time in


100ml water each



Deviation

60 7.0 6.9 6.9 7.0 7.0 0.057735

120 6.3 6.4 6.3 6.3 6.3 0.050000

180 6.0 6.1 5.9 6.1 6.0 0.095743

240 5.7 5.7 5.7 5.8 5.7 0.050000

300 5.5 5.6 5.5 5.5 5.5 0.050000


Average = (7.0 + 6.9 + 6.9 + 7.0) / 4 = 7.0.


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Graph 2.2: average pH levels for Lipton Darjeeling Tea.


0

1

2

3

4

5

6

7

8

60 120 180 240 300

Ave

rage

pH

leve

l of

the

dri

nk

±0.

1

Brewing time in seconds±0.1s

pH levels against brewing time.

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Taj Mahal.

Table 3.1: mass of caffeine extracted in mg±0.1mg from Taj Mahal tea.

Brewing time in


100ml water each



Deviation

60 57.6 58.4 58.7 57.9 58.15 0.493229

120 64.3 64.3 65.1 64.7 64.60 0.382971

180 69.8 71.0 70.3 70.5 70.40 0.496655

240 73.2 73.1 73.6 73.1 73.25 0.238048

300 79.8 80.0 79.7 80.3 79.95 0.264575


Average = (57.6 + 58.4 + 58.7 + 57.9) / 4 = 58.15.

Standard deviation was calculated using a function on Microsoft excel)

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Graph 3.1: average mass of caffeine extracted in mg±0.1mg from Raj Mahal tea.


0

10

20

30

40

50

60

70

80

90

60 120 180 240 300

Ave

rage

mas

s of

caf

fein

e ex

trac

ted

in m

g ±

0.1m

g



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Table 3.2: pH levels for Taj Mahal tea.

Brewing time in


100ml water each



Deviation

60 5.1 5.2 5.1 5.1 5.1 0.050000

120 4.9 5.0 4.8 4.9 4.9 0.081650

180 4.6 4.6 4.8 4.6 4.7 0.100000

240 4.7 4.6 4.7 4.6 4.7 0.057735

300 4.6 4.6 4.7 4.5 4.6 0.081650


Average = (5.1 + 5.2 + 5.1 + 5.1) / 4 = 5.1.


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Graph 3.2: average pH levels for Taj Mahal tea.


4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

5

5.1

5.2

60 120 180 240 300

Ave

rage

pH

leve

l of

the

dri

nk

±0.

1



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Brooke Bond Red Label.

Table 4.1: mass of caffeine extracted in mg±0.1mg from Brooke Bond Red Label tea.

Brewing time in


100ml water each



Deviation

60 54.6 53.8 54.3 54.5 54.3 0.355903

120 60.4 61.1 60.6 60.8 60.73 0.298608

180 64.9 65.0 65.7 65.4 65.25 0.369685

240 72.3 72.4 71.8 72.0 72.13 0.275379

300 76.1 75.9 76.3 76.1 76.10 0.163299


Average = ( 54.6 + 53.8 + 54.3 + 54.5 ) / 4 = 54.3.

Standard deviation was calculated using a function on Microsoft excel)

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Graph 4.1: average mass of caffeine extracted in mg±0.1mg from Brooke Bond Red Label tea.


0

10

20

30

40

50

60

70

80

90

60 120 180 240 300

Ave

rage

mas

s of

caf

fein

e ex

trac

ted

in m

g ±

0.1m

g


Mass of caffeine extracted against time.

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Table 4.2: pH levels for Brooke Bond Red Label tea.

Brewing time in


100ml water each



Deviation

60 5.5 5.5 5.6 5.4 5.5 0.081650

120 5.2 5.2 5.3 5.2 5.2 0.050000

180 5.1 5.2 5.0 5.1 5.1 0.081650

240 4.9 5.1 4.9 5.0 4.9 0.095743

300 4.9 5.0 4.9 4.9 4.9 0.050000


Average = (5.5 + 5.5 + 5.6 + 5.4) / 4 = 5.5.


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Graph 4.2: average pH levels for Brooke Bond Red Label tea.


4.4

4.6

4.8

5

5.2

5.4

5.6

5.8

60 120 180 240 300

Ave

rage

pH

leve

l of

the

dri

nk

±0.

1



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33

Table 5.1: average mass of caffeine extracted from all four brands of tea with different brewing

times.

Brewing time in

seconds of 2g tea

in 100ml water

each

Tea Brands

Twinnings

Earl Grey

Lipton

Darjeeling

Tea

Taj

Mahal

Brooke

Bond Red

Label

60 15.95 45.68 58.15 54.30

120 17.78 54.83 64.60 60.73

180 21.43 63.95 70.40 65.25

240 22.80 72.98 73.25 72.13

300 29.38 88.95 79.95 76.10

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Plotting this on a graph, we can compare the average mass extracted from each brand.

Graph 5.1: average mass of caffeine extracted in mg±0.1mg from all four tea brands.

0

10

20

30

40

50

60

70

80

90

100

60 120 180 240 300

Ave

rage

mas

s of

caf

fein

e ex

trac

ted

in m

g ±

0.1m

g


Average mass of caffeine extracted against brewing time

Lipton Darjeeling Tea

Twinnings Earl Grey

Brook Bond Red Label

Taj Mahal

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Table 5.2: average pH level of all four brands of tea with different brewing times.

Brewing time in

seconds of 2g tea

in 100ml water

each

Tea Brands

Twinnings

Earl Grey

Lipton

Darjeeling

Tea

Taj

Mahal

Brooke

Bond Red

Label

60 5.4 7.0 5.1 5.5

120 5.0 6.3 4.9 5.2

180 5.0 6.0 4.7 5.1

240 5.0 5.7 4.7 4.9

300 4.9 5.5 4.6 4.9

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Plotting this on a graph, we can compare the average pH level of each brand.

Graph 5.2: average pH levels of all four brands.

0

1

2

3

4

5

6

7

8

60 120 180 240 300

Ave

rage

pH

leve

l of

the

dri

nk

±0.

1


Average pH levels against brewing time.

Lipton Darjeeling Tea

Twinnings Earl Grey

Brook Bond Red Label

Taj Mahal

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37

Qualitative Analysis:

The color of the tea solutions increased with brewing time, displaying that the

longer the tea was allowed to boil with the water, the more of its nutrients,

minerals, colors and fluids diffused out of the leaves and into the water. The

chemicals here include caffeine.

The NaOH crystals were white in color, and once added to the beaker containing

water turned the solution a cloudy white. Once the NaOH was dissolved

completely, the solution became transparent.

The NaOH, once combined with water, had a very soapy feel.

The chloroform was a transparent liquid and had a slightly strong smell. However,

the smell was not strong enough to cause anyone to faint. It was freezing cold

when it came in contact with my skin.

The chloroform, when added to the tea solution in the separating funnel settled

distinctly below the tea forming two clear levels: the less dense dark brown tea

above and the transparent, denser chloroform at the bottom.

In between the two layers of the chloroform and the tea was a thin layer of light

brown bubbles.

Upon shaking back and forth, the separating funnel depicted three layers: the tea,

the chloroform, and the glittery organic layer of the tea in the middle. Holding the

funnel to the light displayed the golden-brown color of this organic layer and its

bubbly nature.

Once the organic layer was placed in the separating funnel and the tea was

discarded of, the NaOH was poured in. This resulted in three layers forming

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38

again, going from a dark brown shade (top) to a white sort of transparent shade

(bottom).

After the separating funnel procedure was completed the remaining solution was

heater. This resulted in the release of a transparent and odorless gas and the

bubbling of the deep brown solution to result in the production of the caffeine

crystals.

The crystals were white and were stuck on the side of the beaker and had to be

scraped off the sides.

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39

Conclusion:

From graph 5.1 we can see that there is, in fact, a general increase in the amount of caffeine

dissolved in the beverage as the brewing time for the tea is increased. However, in graph 5.2 we

see a decrease in the pH level, which tells us that tea becomes more acidic as the brewing time is

increased.

My hypothesis has been proven correct since there is an increase in both the caffeine content in

the tea and the acidity as the brewing time is increased. The tea brand which had the highest

caffeine content after 300 seconds of brewing was Lipton Darjeeling Tea, the average mass of

caffeine extracted being 88.95mg. The tea brand with the lowest pH (highest acidity) after 300

seconds of brewing was Taj Mahal.

The general increase of the caffeine content in the tea with the increase in the brewing time is

probably due to the fact that the longer the leaves are left in the water, the more the caffeine

molecules that diffuse out into the water. Since it has a relatively high boiling point (178°C), it

does not evaporate and leave the beverage during the boiling process and so it remains

concentrated in the liquid. However, the increase in acidity (decrease in pH level) is probably

due to two entirely different molecules: oxalate and citrate ions. The same reason applies here:

the longer the brewing time, the more oxalate and citrate molecules diffuse out of the tea leaves

and into the water.

Citrates are molecules associated with citric acid, which is a commonly known organic acid.

Oxalates are commonly found in various leafy vegetables.9

9. “Acidity of Tea,” Rate Tea, accessed September 10, 2013, http:// ratetea.com/topic/acidity-of-tea/79/.

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The results of this experiment show that caffeine content and acidity both increase with the

increase of the brewing time for tea. This data can be used to determine which brand and what

brewing time is best suitable for consumption. For example, Twinnings Earl Grey has the least

amount of caffeine when compared with the other three brands, since even after 300 seconds of

brewing it has only 29.38mg of caffeine whilst Lipton Darjeeling Tea has 88.95mg, the

difference being 59.57mg, which is huge. But although Lipton Darjeeling Tea is the richest in

caffeine content, it is the least acidic. Surprisingly, after 60 seconds of brewing, it had a pH of

7.0 while the other tea brands had an average pH of around 5.3. Even after 300 seconds of

brewing, Lipton Darjeeling Tea didn’t reach that level of acidity.

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Evaluation of weaknesses and improvements:

This investigation contained a few weaknesses and limitations. For example, the method I used

for the extraction of the caffeine was not actually the professional method, which is why the

results may have been slightly less precise. One investigation compared the caffeine content

present in about twenty different brands of tea ranging from Bigelow Cranberry Apple Herb Tea

to Exotica China White. The investigators dipped tea bags of each of the twenty brands into

different volumes of water (6 oz and 8 oz) and used brewing times of 1 minutes, 3 minutes and 5

minutes and found that the caffeine content in the tea increased with the brewing time. Since this

investigation was not conducted in India, the tea brands analyzed are not the same as I have used.

However, Twinnings Earl Grey is a common brand. Their data is as follows:10

10. Chin, Merves, Goldberger, Sampson-Cone and Cone, “Caffeine content of brewed teas,” Oxford Journals.accessed September 28, 2013.

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42

If I compare their readings for the brand of Twinnings Earl Grey with the readings I obtained,

not much of a difference is seen. However, my values are a spread across a slightly wider range.

Their value for the amount of caffeine obtained after a 1 minute steeping time is 19mg while my

average for the same steeping time is 15.95mg, which is 3.05 mg less than what they found. The

reason for this may be that this experiment used the method of liquid-liquid extraction and gas

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43

chromatography with nitrogen-phosphorous detection. However, since this apparatus was too

advanced and was not available in my school laboratory, I researched and found an easier

method online. This method uses chloroform as the main solvent to dissolve the organic layer

from the tea, to which sodium hydroxide and water are added to extract the caffeine.

This investigation also analyzed several different types of tea, such as black, green and white. I

chose to investigate on only black tea since this is the most common type of tea drunk in India.

Another weakness I found in my investigation was the use of the glass trough in order to cool the

tea to about 34.C. Although there are many water baths in my school laboratory, none was large

enough to hold multiple beakers or even one since they were test tube baths, which is why I used

a glass trough filled with cold water. If a large water bath would have been available, the tea

would’ve cooled much faster, thus allowing me to conduct more readings on maybe a few more

brands.

A random error occurred during the process of the caffeine extraction when I had to shake the

separatory funnel back and forth ten times after adding the chloroform and remove the organic

layer. The thin line between the organic layer and the remnants of the tea was hard to see since I

wasn’t very distinct. Because of this I feel that in some trials a few drops of the remnants may

have gone into the organic matter, which could have a small effect on the readings. The only way

to avoid this would have been to use the liquid-liquid extraction and gas chromatography with

nitrogen-phosphorous detection method.

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44

Evaluation of data:

Twinnings Earl Grey tea was shown to have the least amount of caffeine, since its caffeine

content ranged from 15.95mg to 29.38mg. The curve of graph 1.1 increases but not linearly.

Graph 1.2 which displays the average pH of Twinnings Earl Grey tea as the brewing time

increases shows a sudden decrease from 60 seconds to 120 seconds. It then stays constant for the

next 120 seconds, and then there’s a drop again from 240 seconds to 300 seconds.

Lipton Darjeeling Tea started off with a low amount of caffeine, but its curve was very steep and

by the time it reached 300 seconds, it had the highest amount of caffeine when compared to the

rest of the three brands, which was nearly 90mg. However, Lipton proved to be the least acidic

tea since its pH was first 7 (which is neutral) and by the end of the 300 seconds it only reached

5.5 while the other brands reached around 4.5.

Taj Mahal only reached up to 80mg, which is 10mg lesser than the highest which was Lipton

Darjeeling Tea. Its curve was less steep and it started off with caffeine content higher than that of

Lipton. But, this was the most acidic brand of tea. It started as low as 5.1 and went down to 4.7

in the first 180 seconds. It was then constant for 60 seconds, after which it dropped down again

to 4.6. Table 3.2 (the table of the pH levels of Taj Mahal) had an anomalous reading of 4.7 in the

first trial for 240 seconds. This is anomalous because the reading for 180 seconds is 4.6 and the

reading for 300 seconds is also 4.6. This error may be a random error caused by lifting the pH

meter out of the tea.

Brook Bond Red Label had an almost linear graph whose caffeine content ranged from 54.3mg

to 76.1mg. Its pH is also very low which makes it very acidic. It is not linear but it stays constant

from 240 seconds to 300 seconds. However it is still less acidic than Taj Mahal.

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45

While researching on the effect of the brewing time on the amount of caffeine present in the tea

and the pH of the tea, I also discovered other substances whose amount varies with brewing time,

which are the antioxidants. Antioxidants are molecules which inhibit the oxidation of other

molecules and are generally good for health since they prevent a chain reaction from occurring in

a cell that could damage it. The tea plant Camellia sinensis contains several types of

antioxidants. As I had done my investigation on the effect of brewing time on caffeine content

and acidity, I decided not to experiment with the antioxidants. So, this extended essay can be

taken further on to analyze the effect on brewing time on the amount of antioxidants present in

the tea.

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46

Bibliography:

Abc. “What’s your poison?.” Accessed September 11, 2013.

www.abc.net.au/quantum/poison/caffeine/caffeine.html.

Chin, Merves, Goldberger, Sampson-Cone and Cone. “Caffeine content of brewed teas.” Oxford

Journals. Accessed September 28, 2013. http://jat.oxfordjournals.org/content/32/8/702.abstract.

Rate Tea. “Acidity of Tea.” Accessed September 10, 2013. http:// ratetea.com/topic/acidity-of-

tea/79/.

Fuller, Thomas. "A Tea From the Jungle Enriches a Placid Village." The New York Times (New

York), April 21, 2008.

ITIS Report. “Camellia sinensis (L. Kuntze).” Accessed October 10, 2013.

http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=506801.

Oxford. “The Isolation of Caffeine from Tea.” Accessed August 2, 2013.

http://www.oxford.net/~mavarod/portal/school/caffeine.html.

Purdue. “Camellia sinensis (L.) Kuntze.” Accessed October 12, 2013.

http://www.hort.purdue.edu/newcrop/duke_energy/Camellia_sinensis.html.

Smith BD, Gupta U, and Gupta BS. Caffeine and activation theory: effects on health and

behavior. CRC Press, 2007.

Van Breda SV., van der Merwe CF., Robbertse H. and Apostolides Z. “Immunohistochemical

localization of caffeine in young Camellia sinensis (L.) O. Kuntze (tea) leaves.” PubMed.

Accessed October 11, 2013. doi: 10.1007/s00425-012-1804-x.

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INTERNAL ASSESSMENT SAMPLE

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1

An Investigation into the Neutralizing Capacities of Different Antacid Syrups

Research Question:

Which of the five commonly used liquid antacids (Digene, Rantac, Mucaine, Ulgel, Gelusil) has the greatest neutralizing capacity? This is measured by measuring the volume of NaOH required to neutralize the excess HCl left in the HCl-antacid mixture and using the technique of back titration, keeping the concentration and volume of HCl (20ml, 1M) and NaOH(1M) and the surrounding temperature and pressure constant.

Introduction:

Excess stomach acidity can be caused by1:

Increased consumption of spicy and oily food

Food rich in fibre content

Stress

Irregular food consumption

Insufficient sleep

Since in India particularly spicy and oily food is prevalent, excess stomach acidity is not uncommon. Therefore, several different brands produce antacids- both syrup/liquid forms as well as tablets. Each of them has a different composition of alkalis and other chemicals. Yet some particular brands, such as Gelusil, are more popular and widespread. A friend of mine was experiencing burning sensation which is called stomach acidity, and she bought the antacid Rantac from a small drug store since it was the only one available at the time. She found this brand ineffective, so I suggested Digene since it seems to be more popular. She instantly felt relief. This lead me to wonder- do the different antacids have different neutralizing capacities, therefore making some more effective than others? Hence I thought of investigating the neutralizing capacities of 5 common liquid antacids- Digene, Rantac, Mucaine, Ulgel, Gelusil- by using back titration to measure the volume of NaOH required to neutralize a mixture of HCl and 5ml of the antacid.

1) "Acid Reflux Disease Symptoms, Causes, Tests, and Treatments." WebMD.http://www.webmd.com/heartburn-gerd/guide/what-is-acid-reflux-disease.

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Antacids used and ingredients in every 5ml

(As taken from the ingredients labels on the bottles)

Gelusil:

Activated Dimethicone 50mg

Magnesium hydroxide 250 mg (paste)

Dried aluminium hydroxide 250mg (paste)

Sorbitol solution 1.25g

Ulgel:

Magaldrate 400mg

Simethicone 20mg

Rantac:

Ranitidine hydrochloride 84mg

Mucaine:

Oxetacaine 10mg

Aluminium hydroxide 0.291g (paste)

Magnesium hydroxide 98mg (paste)

Digene:

Aluminium hydroxide 0.380g (paste)

Sorbitol solution 1.25g

Simethicone 0.98g

Background Information:

Antacids are drugs that help to combat excess stomach acidity2. The stomach naturally produces between 20ml and 100ml3 of hydrochloric acid (HCL) of pH

2) Brown, Catrin. Higher Level Chemistry: Developed Specifically for the IB Diploma. Pearson, 2009.888-889. 3) "Average Amount of Stomach Acid in the Human Stomach." LIVESTRONG.COM. July 28, 2015.http://www.livestrong.com/article/476461-average-amount-of-stomach-acid-in-the-human-stomach/.

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between 1 to 24, but several factors as listed above could cause the stomach cells to secrete even more than 100ml of HCl, thereby decreasing the pH. Too much acidity can cause pain and ulcers, so antacids must be taken to bring the pH back to the normal level. The antacids work by neutralizing the HCl, so relieving the symptoms. They are usually weakly basic compounds, often metal oxides, hydroxides, carbonates or hydrogencarbonates. The alkali reacts with HCl to produce salt and water, so it neutralizes the acid and cures excessive acidity:

Mg(OH)2 + 2HCl → MgCl2 + 2H2O

This investigation utilizes the technique of back titration to determine the neutralizing capacity of an antacid. Titration is a method where one reactant is poured through a burette to another reactant, and the end-point is generally determined using an indicator5. Back titration is one type that uses a two step process6:

1. Reactant A is made to react with excess of reactant B which is of a pre-determined concentration.

2. A titration is performed to find the amount of reactant B in excess.

This experiment is an application of back titration- HCl would be reactant B, the alkali present in the antacid would be reactant A and the titrant is NaOH. For example if we take the alkali in the antacid to be Mg(OH)2 the reactions would occur as follows:

Mg(OH)2 + 2HCl → MgCl2 +2H2O

HCl + NaOH → NaCl + H2O

Research Question:

Which of the five commonly used liquid antacids (Digene, Rantac, Mucaine, Ulgel, Gelusil) has the greatest neutralizing capacity? This is measured by measuring the volume of NaOH required to neutralize the excess HCl left in the HCl-antacid mixture and using the technique of back titration, keeping the concentration and volume of HCl (20ml, 1M) and NaOH(1M) and the surrounding temperature and pressure constant.

Hypothesis

According to me, Gelusil should have the greatest neutralizing capacity considering the fact that it has the most amount of alkali in a 5ml sample.

4) "Average Amount of Stomach Acid in the Human Stomach." LIVESTRONG.COM. July 28, 2015. http://www.livestrong.com/article/476461-average-amount-of-stomach-acid-in-the-human-stomach/. 5) "What Is a Titration." ? http://chemed.chem.purdue.edu/genchem/lab/techniques/titration/what.html. 6) "Back Titration (Indirect Titration) Calculations." Chemistry Tutorial : Back (Indirect) Titration Calculations. http://www.ausetute.com.au/backtitration.html.

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Variables:

Independent variable- different brands of liquid antacid (Digene, Rantac, Mucaine, Ulgel, Gelusil)

Dependent variable- neutralizing capacity of different antacid by measuring the volume of NaOH required to neutralize excess HCl left in the HCl-antacid mixture

Controlled variables:

Temperature and pressure of the room and reactants

Volume of HCl (20ml ± 0.5ml)

Concentration of HCl and NaOH (1M)

Volume of antacid syrup added (5ml)

Time period for which antacid was mixed into HCl for (30s ± 0.01s)

Same apparatus

Methods of Control:

Temperature and pressure were kept constant by taking all readings on thesame day in the same room, with the temperature set on the air conditioner at24°C.

The volume of HCl was kept constant during each trial by obtaining 20mlusing the same measuring cylinder (25ml ± 0.5ml).

The concentration of HCl and NaOH were maintained by obtaining allsamples from the same bottle for each reading.

20ml of HCl was measured out in the same measuring cylinder each trial, aswas 5ml of the antacid.

A stopwatch was used as a timer to keep the time antacid was mixed into theacid (30s) constant throughout trials.

Materials and Apparatus:

Measuring cylinder capacity 25ml ± 0.5ml

Measuring cylinder capacity 10ml ± 0.2ml

Burette capacity 50ml ± 0.1ml

Clamp and stand

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5

Stirring rod

Funnel

Phenolphthalein indicator (5 drops per trial)

1M Hydrochloric acid

1M Sodium hydroxide

Stopwatch (± 0.01s)

100ml conical flask

Methodology:

1. Attach the burette (50ml ± 0.1ml) to the clamp and stand, making sure it is held slightly above the surface.

2. Fill the burette (50ml ± 0.1ml) from above using a funnel all the way till the 0ml mark at the top with the 1M NaOH solution.

3. Measure 20ml of HCl in the measuring cylinder (25ml ± 0.5ml) and pour this into the 100ml conical flask.

4. Measure 5ml of the antacid in the measuring cylinder (10ml ± 0.2ml) and pour this also into the conical flask (100ml).

5. Set a timer on the stopwatch (± 0.01s) for 30s and start stirring the mixture in the conical flask (100ml) until the timer rings.

6. Add five drops of phenolphthalein indicator into the mixture in the conical flask (100ml) and stir again gently.

7. Place the conical flask (100ml) underneath the opening of the burette (50ml ± 0.1ml).

8. Turn open the tap of the burette so the NaOH flows gently.

9. Keep stirring the mixture in the flask by gently shaking it.

10. Closely watch the colour of the mixture in the conical flask.

11. When the mixture turns into a light pink colour, quickly close the tap of the burette.

12. Read and note the volume of NaOH that was dispensed.

13. Top off NaOH in the burette so it is back all the way up to the 0ml marking.

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6

14. Wash away the contents of the conical flask.

15. Repeat steps 2-14 four more times for the same antacid

16. Repeat the procedure for all the different antacids (Gelusil, Digene, Rantac,Mucaine, Ulgel)

17. Enough data (25 readings) have now been collected to process the data,keeping the conditions of the experiment constant.

Safety Considerations:

Make sure the tap on the bottom of the burette is tightly closed. Wear glovesand lab coat as NaOH is corrosive and will burn skin if dropped. It must not beingested.

HCl is also corrosive so it must be handled carefully and must not beingested.

Do not stir too vigorously, as corrosive HCl could come out of the conical flaskand onto skin, causing pain.

If HCl falls on one’s skin, they must wash with water and soap immediately.

Qualitative Analysis:

Digene and Gelusil were pink in colour, Mucaine and Ulgel were green andRantac was yellow.

There was effervescence when Mucaine was added to the HCl

Digene was not soluble at all in HCl so since it was difficult to judge the end-point of the neutralization reactions, results could not be obtained for thisantacid.

Ulgel was able to mix to some extent so results could be otained

The antacids retained their colours when mixed with HCl

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7

Raw and Processed Data- Table 1:

Volume of NaOH need to neutralize Antacid-HCl mixture

Volume of NaOH dispensed from burette (ml ± 0.1ml) Type of Antacid

Trial 1

Trial 2 Trial 3 Trial 4 Trial 5 Mean

Standard deviation

Gelusil 3.5 3 1.4 2 1.7 2.3 0.8927 Ulgel 3 1.6 2.8 2.9 2.1 2.5 0.6058 Digene N/A N/A N/A N/A N/A N/A N/A Rantac 10.6 20.5 7.9 8 7.3 10.9 5.5365 Mucaine 9.2 6.1 7.2 7.1 7 7.3 1.1389

Sample Calculations

The data above must be processed in order to obtain meaningful results from it. Since there were five trials taken, we will use the mean of these trials in calculations. We will calculate the number of moles of alkali in each of the antacids.

1M is equal to 1 mol/dm3. Hence, we can calculate the number of moles in 20ml of HCl by using the formula:

𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑠 = 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 × 𝑉𝑜𝑙𝑢𝑚𝑒

20ml= 0.02 dm3

The number of moles of HCl= 1 x 0.02= 0.02 mol

In this experiment it is assumed that the number of moles of alkali to neutralize HCl is equal to the number of moles of HCl. The concentration of NaOH is also 1 mol/dm3. Let us take the mean of the NaOH dispensed for Gelusil to calculate the number of moles of NaOH here:

Number of moles of NaOH dispensed= 0.0023 x 1= 0.0023mol

Now we can find the moles of alkali in the antacid sample by subtracting the number of moles of NaOH from 0.02:

No. of moles of alkali in antacid= 0.02-0.0023= 0.0177mol

Number of moles of alkali in antacid- Table 2

Antacid Mean NaOH dispensed (dm3 ± 0.0001dm3)

Moles of HCl (mol)

Moles of NaOH (mol)

Moles of alkali in antacid (mol)

Gelusil 0.0023 0.02 0.0023 0.0177 Ulgel 0.0025 0.02 0.0025 0.0175 Rantac 0.0109 0.02 0.0109 0.0091 Mucaine 0.0073 0.02 0.0073 0.0127

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Total Percentage Uncertainty

𝑃𝑒𝑟𝑐𝑒𝑛𝑡𝑎𝑔𝑒 𝑢𝑛𝑐𝑒𝑟𝑡𝑎𝑖𝑛𝑡𝑦 = (𝑁𝑒𝑡 𝑢𝑛𝑐𝑒𝑟𝑡𝑎𝑖𝑛𝑡𝑦

𝑀𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑣𝑎𝑙𝑢𝑒) × 100%

The net uncertainties for NaOH dispensed, volume of antacid and volume of HCl were mentioned above, and can be summarized in the following expression respectively for 20ml of HCl and 5ml of antacid. The volume of NaOH dispensed varies so its given the variable x. The uncertainty of the burette has been converted to dm3 since that is the unit used in the calculations. The total percentage uncertainties for each volume of NaOH dispensed is calculated in the following table.

0.5

20× 100 +

0.2

5× 100 +

0.0001

𝑥× 100

= ± (6.5 +0.1

𝑥) %

Percentage Uncertanties- Table 3

Antacid Mean NaOH dispensed (dm3 ± 0.0001dm3)

Percentage uncertainty of NaOH dispensed

Total percentage uncertainty

Gelusil 0.0023 ±43.4783% ±49.9783% Ulgel 0.0025 ±40.0000% ±46.5000% Rantac 0.0109 ±9.1743% ±15.6743% Mucaine 0.0073 ±13.6986% ±20.1986%

Absolute Uncertainty

Absolute uncertainty can be calculated by multiplying the total percentage uncertainty to the volume of NaOH dispensed in dm3.

In the case of Gelusil,

49.9783 x 0.0177= 0.8846 mol is the maximum number of moles that can be more or less than the value written in table 2 (0.0177)

Absolute Uncertainties- Table 4

Antacid Absolute Uncertainty (mol)

Gelusil 0.8846 Ulgel 0.8138 Rantac 0.1426 Mucaine 0.2565

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9

With all of the data processed above, a line graph can be produced to compare the number of moles of alkali in each of the antacids, using this experiment’s values.

Graph 1

Analysis of Graph 1-

From this graph, it is evident that Gelusil, closely followed by Ulgel, contains the largest number of moles of alkali out of these four antacids. Therefore, it also has the largest neutralizing capacity. Rantac contains the least number of moles of alkali so it has the least neutralizing capacity. Mucaine has slightly more than Rantac but less than Ulgel. The error bars show absolute uncertainty as calculated in Table 4 above.

The results can also be plotted on a bar graph:

Graph 2

Similar results to those shown by Graph 1 are also portrayed by Graph 2. These error bars also show absolute uncertainty as calculated in Table 4.

0

0.005

0.01

0.015

0.02

0.025

0.03

Gelusil Ulgel Rantac Mucaine

No

. of

mo

les

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Different Brands of Antacid

Number of moles of alkali in antacid (mol)

0

0.005

0.01

0.015

0.02

0.025

0.03

Gelusil Ulgel Rantac Mucaine

No

. of

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Different Brands of Antacid

No. of Moles of alkali in antacid (mol)

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Conclusion

It is clear from the experimental values and from the graph that Gelusil has the strongest neutralizing capacity, followed by Ulgel and Mucaine, and Rantac has the least strong neutralizing capacity. The final values for the number of moles of alkali in 5ml of Gelusil, Ulgel, Rantac and Mucaine are 0.0177mol, 0.0175mol, 0.0091mol and 0.0127mol respectively. From these values it is clear that Gelusil has the most number of moles of alkali in a 5ml sample and so it has the greatest neutralizing capacity, while Rantac has the lowest. Gelusil and Ulgel contain an almost equal number of moles of alkali in the 5ml sample so have a nearly equal neutralizing capacity. Rantac has the least number of moles and the lowest neutralizing capacity of the four- 0.0091mol. Mucaine was in the middle. Results could not be obtained for Digene due to it being insoluble in HCl.

These results confirm the hypothesis- Gelusil has the most number of moles of alkali in it and this can even be seen in the ingredients- it contains a high amount of both aluminium and magnesium hydroxide. Therefore, it has the greatest neutralizing capacity. Percentages of total uncertainty were also different for each antacid. The more the number of moles of alkali was, the higher the percentage uncertainty, ranging from ±49.9783% for Gelusil to ±15.6743% for Rantac. This is because the mean volume of NaOH dispensed for Gelusil was 0.0023 dm3, but for Rantac it was 0.0109 dm3- nearly five times as much. The reason for the low neutralizing capacity of alkali in Rantac can be explained by its ingredients- it only has ranitidine hydrocholoride, which is not an alkali but instead prevents ulcers in the stomach by working on the cells that produce HCl.

Evaluation

The extremely large percentage errors calculated in this experiment indicates that this experiment has some flaws. These large values, however, could be linked back to the conversion of the volume of NaOH dispensed from ml to dm3, which was necessary in order to calculate the number of moles. The set up itself was well designed for gathering the data and it was simple to replicate, so there is low chance of systematic error. The number of trials should be a minimum of 5 to make any proper judgement, and all 5 trials were executed.

The different results of the trials for same antacid are precise- they are more or less similar as seen by the standard deviations given in table 1. The standard deviation for Rantac is slightly higher- this could be due to random errors causing anomalies.

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The uncertainties of the equipment were not too large as noted above. The main reason for the large uncertainty is the conversion of the NaOH dispensed from ml to dm3. Otherwise, there is not really much room for error.

Since the NaOH and HCl solutions were not prepared specially for this experiment- they came directly from a bottle in the lab- it is not ensured that they are of 1M concentration. Their concentration itself could have an uncertainty- leading to inaccuracy of final results.

The error bars on the graph show absolute uncertainty as was calculated in Table 4. They are quite large, and are a result of the large percentage uncertainties. As stated above, the large values for percentage uncertainties are mostly because of the unit conversion of NaOH, as well as the time delay before the faucet was entirely closed.

There’s also a possibility of random errors in this experiment. These errors, however, are much harder to evaluate properly and control.

Weaknesses and Improvements

The main flaw of this experiment was the difficulty in judging the colour change of the phenolphthalein. This is because of the antacid’s colours- Gelusil in fact is a bright pink colour, making it very hard to tell when all the acid had been neutralized. Ulgel did not dissolve entirely, so only certain regions in the mixture turned pink while others remained colourless.

Judging when to close the faucet of the burette forms majority of the percentage error. After sensing a colour change, there could be a slight time delay before the faucet can be entirely closed- so more NaOH may be dispensed than needed.

Improvement How it improves the investigation Use ground up antacid tablets Won’t show colour, will dissolve

completely in HCl Have another person immediately close the burette once you signal that there has been a colour change

Reduced error from human reaction time

Heat up mixture to 370C and perform experiment

Antacids are made to act as this temperature as it closer to the temperature in the stomach

Dilute the antacids with the same volume of water

The colour of the antacid will be less prevalent so the colour change will be easier to spot

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Extension of the lab

There is scope for further investigation into this experiment to obtain more information on the subject. Other antacid liquids that are available could also be used, and perhaps one of them has a greater neutralizing capacity than Gelusil. Using a similar methodology, the number of moles of acid or alkali in other medicines could also be determined. Maybe it could be found for certain foods and drinks (like fizzy drinks) as well, and the results can be linked to the causes of stomach acidity and other health issues.

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Resources used

1.Text Books:

a)Pearson’s

2.Reference Books

a)Oxford IB Chemistry

b)Cambridge IB Chemistry

3.Various websites like

(i) intro.chem.okstate.edu/1314F00/Lecture/Chapter10/VSEPR.html- VSEPR Theory and Shapes of the molecule. (ii) https://www.youtube.com/watch?v=lD1za3warmw-Conjugate acid and bases

4.Past IB papers

5.Teacher’s worksheets

c)Dot Point

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Documents

CHEMISTRY HANDBOOK - Symbiosis International School