Learning Area : Electrochemistry

Topic : Electrolysis in Aqueous Solutions

Date : 10th March 2011

Class : 4 Einstein

Time : 40 minutes

No. of students : 10

Learning Objective : Analysing the electrolysis of aqueous solutions

Learning Outcomes : Students should be able to :

a) Identify the cations and anions in an aqueous solutions.

b) Describe the electrolysis of an aqueous solutions.

c) Write half equations for the discharge of ions at anode and cathode.

Science Process Skills :

Scientific Attitudes and Noble values:

Thinking Skills :

Prior Knowledge : a) Students had already learned about the periodic table in Chapter 4.

(Metal and non-metal elements)

b) Students already learned about electrolytes and non-electrolytes.

c) Students had discovered the electrolysis in molten compound.

Teacher’s References : i) Websites:

http://www.gcsescience.com/ex.htm

http://www.myadvocators.com/chemistry/quick-revision-series/electrolysis/electrolysis-

of-aqueous-solutions/

ii) Books:

Chemistry Form 4, Integrated Curriculum For Secondary Schools

Low swee Neo, Lim Yean ching, Eng Nguan Hong, Lim Eng Wah and umi Kalthom binti

Ahmad, 2005.

Laboratory Manual :Green Chemistry An Approach That Addresses Education for

Sustainable Development.

Mageswary Karpudewan, Zurida Hj Ismail and Norita Mohamed, 2009/2010.

Student’s References : Books

Chemistry Form 4, Integrated Curriculum For Secondary Schools

Low swee Neo, Lim Yean ching, Eng Nguan Hong, Lim Eng Wah and umi Kalthom binti

Ahmad, 2005.

Lesson Plan:

Step Content Teacher’s Activity Student’s Activity Remarks

Step 1

(± min)

Induction set Teacher asks students :

a) definition of electrolysis.

b) definition of electrolytes.

With the help of diagram, teacher

asks students to recall the 3 main

components in electrolysis process.

Students recall back what they

learned in previous lesson :

Expected answer :

a) A process whereby an

electrolyte is broken down

into its constituent elements

with the help of electric

current.

b) Electrolytes are substances

that can conduct electricity.

Students review back the 3 main

components based on electrolysis in

molten compound that they learned

in previous topic.

Expected answer :

1) Electrolytes

2) Direct current (battery)

3) Electrodes

Teaching aids:

Whiteboard

Manila card

Power point

Periodic Table

Aims :

a) Actively

engage

students with

teaching and

learning

process.

b) To induce

students to

make use the

previous

lesson and

make

Using the diagram before, teacher

discuses generally the electrolysis

in molten compound using NaCl as

electrolytes. (What happen to this

NaCl electrolyte if I heat it up?)

Teacher pause the lesson and asks

students weather they still

remember how to determine which

the elements that will form cations

and which elements will form

anions?

e.g NaCl

Na+ = Metal element

Cl- = Non-metal element

Teacher asks students the number

of ions present in the molten

electrolytes after the electric current

is passed through it.

Students express their opinion about

molten compound.

(Expected answer : NaCl electrolytes

will melting)

Students recall back what they

learned in the Chapter 4 of Periodic

Table.

Expected answer :

All metals form cations while non-

metal will form anions.

Expected answer :

Two types which are Na+ and Cl-.

connection

between the

previous

topic with the

new lesson.

c) To help

students get a

better idea by

using the

manila card.

Teacher asks students to identify

what happen to the electrolyte if

instead of melt it up the water is

add up into the beaker.

Teacher asks students how many

types of ions will present in the

aqueous solution electrolytes.

Teacher guide the students to

identify the topic to be covered in

the teaching and learning process.

Students respond to teacher by state

that the electrolytes will dissolve in

the water and become an aqueous

solution.

Expected answer :

Four types of ions which are Na+,

Cl-, H+, and OH-.

Students can identify that they are

going to learn about electrolysis in

aqueous solution.

Step 2

(± min)

Identify cations and

anions in aqueous

solutions.

Teacher show a video on

electrolysis process of NaCl

solutions. Teacher asks students to

take note the type of ions present i

n the animation and the movements

of the ions to their respective

electrodes.

Based on the video, teacher give

Students observed the video

critically.

Students give appropriate responses

Teaching aids:

1. Power point

2. Whiteboard

3. Manila cards

4. Diagram

5. Worksheets

series of questions:

a) What are the ions present in

the video?

b) What is the similarity

between H+ and Na+ ions?

c) What is the similarity

between OH- and Cl- ions.

d) Where do the positive

charge ions go?

e) Where do the positive

charge ions go?

Teacher explains the difference

between anode, anions cathode,

and cations using an analogy of a

boy and a girl. (the electrodes is

named differently because they are

attached to different terminal of DC

(battery))

With the aids of diagrams teacher

tells students that the boy and girl

to teacher.

Expected answer :

a) Na+ H+ Cl- OH-

b) Both are positive ions

(cations)

c) Both are negative ions

(anions)

d) Positive ion goes to cathode.

e) Negative ion goes to anode.

Student analyses teacher’s

explanations about the analogy that

represents the movements of anions

to anode and cations to cathode.

Aims:

1. The use of

analogy is to

reinforce

students

understandin

g that a

different sign

of electrodes

will attract

different sign

of ions.

will represent the electrodes :

Girl = Anode

Boy = Cathode

Teacher asks students :

a) In your opinion, a girl will

attract to a boy or a girl?

b) So, these two little boys will

represent which ion? Cation

or anion?

c) Based on your opinion, how

about the boy? Who will

they attract to?

d) So, these two little boys will

represent which ion? Cation

or anion?

*Boy = Cathode and cations

Girl = Anode and anions

Teacher guides students to make a

conclusion that the different sign of

cathode (-ve sign) will attract a

Expected answer :

a) Boy

b) Anions

c) Girl

d) Cations

Students review the analogy to be

applied into the real cases of

movements of ions towards their

opposite sign of ions (cations +ve

sign).

Teacher gives an activity to the

students to familiarize them with

the different types of electrolytes.

Activity 1 : (Drill and Practice

Puzzles)

a) CuSO4 solution

b) ZnCl2 solution

c) PbBr2 solution

d) MgSO4 solution

Teacher gives a tip on how to

remember that cations are positive

charge and anions are negative

charge.

The tip is :

Cations

respective electrodes.

Students practice their understanding

in determine the cations and anions

and their movement towards anode

or cathode. Drill practice puzzle.

Expected answer :

Cathode

(cations)

Anode

(anions)

a) Cu2+ H+ SO42- OH-

b) Zn2+ H+ Cl- OH-

c) Pb2+ H+ Br- OH-

d) Mg2+ H+ SO42- OH-

Students will employ the tip to

prevent them from interchange the

positive and negative sign of the

charges.

The letter ‘t’ in the middle of

cations will represent the positive

sign of the ions.

Anions

Anions is stands for A Negative

Ions

Step 3

(± min)

Effect of positions of

ions in

electrochemical series

Teacher asks students to recall back

the analogy of a boy and a girl in

explaining the movements of

electrons in aqueous solutions.

Teacher encourage the student to

think critically and creatively by

saying :

a) In this case there are two

girls at the cathode right,

but which one will be

choose by cathode?

b) The same goes at the anode

because there exist two boys

and how can we know

which one will be choose by

Students recall back the analogy.

Students respond to teacher

accordingly.

Expected answer :

a) The one that are more pretty

or kind etc.

b) The one that are more

handsome and macho etc.

anode?

Teacher asks students to apply the

concept in the analogy into

electrolysis process. (instead of

how pretty or handsome the ions

are, in electrolysis we will

determine which ions will be

choose to further react by looking

at its ease of discharges abilities)

Teacher shows Electrochemical

Series Diagram and help students to

make a mnemonic in order to make

it easy to remember.

Cation (up) Mnemonic

K+ Kalau

Na+ Nak

Ca2+ Cantik

Mg2+ Macam

Students will apply the balloon

analogy into half equations of

electrolysis in aqueous solutions.

Al3+ Angelina

Zn2+ Zuli

Fe2+ Faustina

Sn2+ Suruh

Pb2+ Pergi

H+ Hutan

Cu2+ Cari

Ag2+ (down) Antu

*the ease of discharge increases

down the series

Anion (up) Mnemonic

F- Fazira

SO42- Suka

NO3- Nak

Cl- Cucuk

Br- Belakang

I - Itik

OH- (down) OMG

*the ease of discharge increases

down the series

Teacher provides another activity

(Activity 2 : Choose The Best) for

the students using the same

electrolytes in Activity 1 (Drill and

Practice).

Teacher asks students to choose the

anions and cations that will react at

anode and cathode based on

electrochemical series using.

a) CuSO4 solution

b) ZnCl2 solution

c) PbBr2 solution

d) MgSO4 solution

Teacher reminds students that they

needs to remember the

electrochemical series and suggest

them to use mnemonic like the

teacher prepared.

Students participate in the activity

critically by firstly discuss it in the

group and later paste the answer on

the whiteboard.

Expected answer :

a) Cathode : Cu2+

Anode : OH-

b) Cathode : H+

Anode : OH-

c) Cathode : H+

Anode : OH-

d) Cathode : H+

Anode : OH-

Step 4

(± min)

Write half equations

for the discharge of

Teacher will introduce the ‘DTD

2E’s Steps’ to the students in order

Students will participate in the

discussion appropriately according to

Teaching aids :

1. Power point

ions at the anode and

cathode.

to illustrate the electrolysis

process :

1- Diagram (draw and label

the electrolysis diagram)

2- Table. (draw a table and

divide the table into two

columns for anode and

cathode)

3- Determine the cations and

anions.

4- Electrochemical Series

(Choose the ions that will

be choose to further react at

anode and cathode)

5- Equations (write equations

and balanced it)

For the last E in DTD 2E’s Steps

teacher will asks :

a) Which ions will donate

electron/s?

b) Which ions will accept

teacher’s instructions.

Students interpret which ions will

donate or accept electrons based on

their understanding about the process

occur at cathode and anode.

Expected answer :

Aims:

1- To test students

understands.

2- To make sure

students actively

involved in the

teaching and

learning process.

3- To activate

students

memorize the

steps in

illustrating

process in

electrolysis

using acronym.

electron/s?

Teacher gives a simple analogy

about the placement of electrons in

the right hand side (RHS) or left

hand side (LHS) of equations.

Let’s assume the electrons are a

balloon.

LHS of half equations is ourselves

and RHS is our friend.

Donate electrons

When we give a balloon to our

friend, of course the balloon will

not be with her or his and not with

us anymore. So, that’s why for

anions that donate electrons the half

equation will place the electron on

the RHS with the products and not

with OH- itself. (no longer be

together with anions that donate

electrons)

a) Anions

b) Cations

e.g :

4OH- (aq) 2H2O(l) + O2(g) + 4e-

Accept Electrons

But if our friends gift us a balloon,

of course the balloon that we accept

will be with us. So, the same goes

for cations when it accepts

electrons the electrons will be

placed LHS of the half equations.

(be together with cations that

accept electrons)

e.g :

Cu2+ (aq) + 4e- Cu(s)

Teacher asks students to think the

movement of electrons in

electrolysis process based on the

donation and accepting electrons

concept.

Step 5

(± min)

Conclusion Teacher re-shows the diagram of

electrolysis in aqueous solution and

guides students to re-explain the

Students give appropriate response to

teacher

process of electrolysis using DTD

2E’s steps using CuSO4 solution

and NaCl solution.

Teacher ask student to recall back

what they have learnt.

a. What is electrolysis of an

aqueous solution?

b. Give me steps in determine

the product in electrolysis

Teacher asks :

a) In your opinion can you

suggest the other factors

that will affect the

electrolysis?

b) What are the applications of

electrolysis in our daily

life?

a. In electrolysis of an aqueous

solution,hydrogen ions,H and

hydroxide ions,OH are also

present in addition to the

anions and cations of the

dissolves compounds.

b. DTD 2E’s steps

Expected answer :

a) Concentrations and types of

electrodes.

b) Rusty, coated brooch and etc.