Chemistry perfect-score-module-form-4-set-3

Set 3 Electrochemistry Perfect Score F4 2010

Electrolysis

1. Define the meaning of electrolyte and non-electrolyte and respective examples.

Electrolyte Non-electrolyte
Meaning

Example

2. Define electrolysis:

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

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

3. Energy change :

Electrolysis: ………………………..….. energy to ………………………………energy.

Voltaic cell: ……………………………..energy to ………..……………………. energy.

4. Write the half equation to represent the discharge of anion and cation.

Anion Half equation Cation Half equation
Hydroxide Hydrogen ion,
ion, OH- H+

Chloride ion, Sodium ion,
Cl- Na+

Bromide ion, Silver ion, Ag+
Br-

Iodide ion, Lead (II)ion,
I- Pb2+

Oxide ion, O2- Copper(II) ion,
Cu2+

Aluminium ion,
Al3+

6. Products of electrolysis depend on three factors, they are

a) ………………………………………………………….…………………………………..………..

b) ……………………………………………………………………………………………………….

c) ……………………………………………………………………………………………………….

Chemistry Perfect Score Module Form 4 2010 Set 3 42


7. Complete the electrochemical series below.

Cation Anion

K+ F-

Ca2+
Cl-

Zn2+

Ease of discharge
+ increases
H

Diagram: Electrochemical Series



Sodium nitrate
solution, 0.5 mol dm-3 Carbon electrodes

Electrolysis of sodium nitrate solution.

8. Describe the electrolysis of sodium nitrate solution using carbon electrodes.

Anode Cathode

Write the formula of all ions
present in the electrolyte.
Write the formula of ion/ions
which is/are attracted to anode
and cathode.

Which is selectively discharged?
Give a reason.

Write the half equation to
represent the discharge.

What will you observe at the
electrode?

Name the product.

State the test to identify the
product.



Potassium chloride
solution, 0.5 mol dm-3
Carbon electrodes

Electrolysis of potassium chloride solution

9. Describe the electrolysis of potassium chloride solution using carbon electrodes.

Anode Cathode

and cathode.

Give a reason.


electrode?

Name the product.



Copper electrode
Iron electrode
Copper(II)nitrate

Electrolysis of copper (II) nitrate solution

10. Describe the electrolysis of copper (II) nitrate solution using metal electrodes.

Anode Cathode

and cathode.

Give a reason.


electrodes?

Name the product.

What will you observe to the
electrolyte?
Explain why?



Voltaic cell / Simple cell

Zinc electrode
Copper
Copper(II)sulphate electrode

11. Describe the voltage cell.

Negative terminal Positive terminal

State all ions present in the
electrolyte.
Identify positive terminal and
negative terminal.
Explain why?

Write half equation at
negative terminal.

Write the formula of ions
which are moved to positive
terminal.

Which is selectively
discharged?
Give a reason.

Half equation at positive
terminal

What will you observe at
negative and positive
terminal?
What will you observe to the
electrolyte?
Explain why?
Overall / Full ionic equation



Application of electrolysis

12. State the aim of electroplating of metal.

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

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

13. The principal of electroplating.
(a) The thing to be electroplating must be ………………………………………………………………...

(b) The electrolyte ………………………………………………….………….…………………………..

(c) The anode ………………………………………………….………….……………………………….

14. To electroplate the spoon with silver.

Iron spoon Silver electrode

Silver nitrate solution, 0.5 mol dm-3

(a) Write the half equation at silver electrode.

…………………………………………………………………………………………………..
(b) Write the half equation at iron spoon.

…………………………………………………………………………………………………..
(c) State the observation at silver electrode.

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

(d) State the observation at the iron spoon.

…………………………………………………………………………………………………..
(e) An even and lasting layer of metal is obtained if:

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

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



15. Purification of metal.
(a) Things to be purified must be at …………………………………………….……………………..

(b) The other electrode ………………………….……………………………………….…………….

(c) The electrolyte ……………………………………………………………………………….…….

The electrochemical series

16. The electrochemical series

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

………………………………………………………………………………………………………..
17. The electrochemical series can be constructed based on;

(a) The potential difference between two metals, in voltaic cell. The higher the voltage value,

the …………………………………………………………………………………………

(b) The ability/ tendency of a metal to displace another metal from its salt solution. A metal

which ………………………………………………… able to displace metal below it in

the series from its salt solution.

PAPER 2: STRUCTURE

1. Diagram 1 show the apparatus set-up used to electrolyze 0.1 mol dm-3 of sodium chloride solution using
carbon electrodes.

Gas Q
Gas P
0.1 mol dm-3 of sodium
chloride solution

Electrode X Electrode Y
_ +

Diagram 1
(a) Name electrodes X and Y.

……………………………………………………………..…………………………………………..
[1 mark]



(b) Write the formula of all ions present in the solution.

…………………………………………………………………….…………………………………..
[1 mark]
(c) (i) Name gas P collected in the test tube.

……………………………………………………………………………………………………..
[1 mark]
(ii) State a chemical test to confirm your answer to (c)(i).

……………………………………………………………………………………………………..
[1 mark]
(iii) Write a half equation for the reaction that takes place at electrode X.

……………………………………………………….…………………………………………..
[1 mark]
(d) (i) Name gas Q collected in the test tube.

…………………………………………………………….………………………………………..
[1 mark]
(ii) State a chemical test to confirm your answer to (d)(i).

……………………………………………………………………………………………………..
[1 mark]
(iii) Write a half equation for the reaction that takes place at electrode Y.

……………………………………………………………………………………………………..
[1 mark]
(e) What difference will it make if the experiment is repeated by using 2 mol dm-3 of sodium
chloride solution? Explain your answer.

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

……………………………………………………………………………………………………..
[2 marks]

2. Diagram 2 shows the apparatus set-up to carry out an electrolysis of aqueous copper(II) sulphate solution.

copper
carbon 0.2 mol dm-3 of elecrodes
electrdes copper(II)
sulphate solution
Experiment I Experiment II
Diagram 2

(a) Write the formula of all the ions present in the copper(II) sulphate solution.

…………………………………………………………………………………………………..
[1 mark]


(b) (i) Name the product produced at the anode in Experiment I.

…………………………………………………………………………………………………..
[1 mark]
(ii) Write a half equation for the reaction that takes place at this electrode.

…………………………………………………………………………………………………..
[1 mark]
(c) (i) Name the product produced at the anode in Experiment II.

…………………………………………………………………………………………………..
[1 mark]
(ii) Write a half equation for the reaction that takes place at this electrode.

…………………………………………………………………………………………………..
[1 mark]

(d) (i) What happen to the intensity of the blue copper(II) sulphate solution in Experiment
I?

…………………………………………………………………………………………………..
[1 mark]

(ii) Explain your answer in (d) (i).

…………………………………………………………………………………………………..
[1 mark]
(e) (i) What happen to the intensity of the blue copper(II) sulphate solution in Experiment
II?

…………………………………………………………………………………………………..
[1 mark]
(ii) Explain your answer in (e) (i).

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

…………………………………………………………………………………………………..
[1 mark]

3. Diagram 3 shows a simple cell

V

electrode Y
electrode X
electrolyte

Diagram 3



Two different electrodes are immersed into an electrolyte. The voltage of the cell is recorded. The
experiment is repeated by using different pairs of electrode. Table 3 shows the results obtained. The
metals of which electrodes V, W, X, Y and Z are made of, for divalent ions.

Experiment Pairs of electrodes Positive terminal Negative terminal Voltage/V
1 X/Y Y X 0.70
2 X/Z X Z 1.05
3 X/W X W 1.55
4 Y/V V Y 0.50
Table 3

(a) Suggest a suitable electrolyte for the above experiments.

…………………………………….…………………………………………………………………..
[1 mark]
(b) State the direction of the flow of electrons in Experiment 1 which used electrodes X and Y.

……………………………………….………….……………………………………………………..
[1 mark]
(c) Write half equation for the reaction that takes place at the negative terminal in Experiment 2 which
used electrodes X and Z.

………………………………………………..………………………………………………………..
[1 mark]
(d) State a hypothesis for the above experiments.

…………………………………………………………………………………………………………..
[1 mark]
(e) Arrange the metals V, W, X, Y and Z in decreasing order in the Electrochemistry Series.

………………………………………………..………………………………………………………..
[1 mark]
(f) A chemical cell is set-up using electrodes Z and V.
(i) State the negative terminal of the cell.

…………………………………………….…………………………………………………………..
[1 mark]
(ii) Calculate the voltage of the cell.

[1 mark]
(g) (i) State the pair of electrodes that will give the highest voltage reading.

…………………………………………………………………………………………………………..
[1 mark]
(ii) Calculate the voltage of the cell.

[1 mark]



PAPER 2 : ESSAY

4. (a) Ethanoic acid solution is electrolysed by using platinum electrode. What is produced at
the cathode? Write a half equation for the reaction that occurs at the cathode.
[2 marks]
(b) Diagram 4 shows Cell X and Cell Y.

V

Zinc plate Copper plate copper electrode

copper(II)
nitrate
Cell X Diagram 4
Cell Y

Cell X is a chemical cell while cell Y is an electrolytic cell. Compare cell X and cell Y.
[8 marks]
(c) A student wants to purify an impure copper plate by the process of electrolysis. Design an experiment in
the laboratory to purify the impure copper plate.
Your answer should include the following:
 materials and apparatus needed
 a diagram with the arrangement of apparatus
 the procedure
 observation
 chemical equation involved
[10 marks]

PAPER 3 : STRUCTURE

5. A student carries out an experiment to study the potential difference between two types of
different metals. The apparatus arrangement used is shown in Diagram 5.

Before experiment After experiment

V V

zinc plate Zinc plate iron plate
iron plate
copper(II) nitrate

Diagram 5



(a) State the observation and inference involved in the experiment in the table below.

Metal plate Observation Inference

Zinc

Iron

(b) The student repeated the experiment by replacing the iron metal with copper metal,
aluminium metal and magnesium metal.

Table 5 shows the voltage reading obtained from the metal pairs.

Metal pairs Negative terminal Positive terminal Voltage/V
Zinc – iron Zinc Iron 0.4
Zinc – copper Zinc Copper 1.1
Zinc – almunium Aluminium Zinc 0.8
Zinc – magnesium Magnesium Zinc 1.4
Table 5

Based on the information above, complete the table below.

Type of variables Action to be taken
(i) Manipulated variables : (i) Way to change the manipulated variables :

___________________________ _________________________________

(ii) Responding variables : (ii) How do these variables respond:

___________________________ _________________________________

(iii) Constant variables : (iii) Way to fix the constant variables :

___________________________ _________________________________

[6 marks]

(c) State the hypothesis of the experiment

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

(d) If the experiment is repeated by using lead metal to replace iron metal, predict the possible
reading recorded by the voltmeter.

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



6. Diagram 6 shows two set-up apparatus used to electrolyzed 0.001 mol dm-3 hydrochloric acid and
1.0 mol dm-3 hydrochloric acid by using carbon electrodes.

Carbon
electrode

1.0 mol dm-3
0.001 mol dm-3 hydrochloric
hydrochloric acid
acid
Diagram 6

(a) State a suitable hypothesis for the experiment.

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

(b) State all the variables involved in the experiment
(i) Manipulated variable

…………………………………………………………………………………………………..
(ii) Responding variable

…………………………………………………………………………………………………..
(iii) Constant variables

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

(c) Write the observations at the anode and cathode for both sets of experiment.

Electrolyte
Set 1 ( 0.001 mol dm-3 Set 2 ( 1.0 mol dm-3
Terminal hydrochloric acid ) hydrochloric acid )

Anode

Cathode

(d) Write half-equation for the discharge of ions at anode for Set 1 and Set 2.

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

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


(e) Predict the observation at the anode and cathode when 0.0001 mol dm-3 potassium
nitrate solution is electrolysed.

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

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

PAPER 3 : ESSAY

7. “Concentration of ions used during electrolysis affects the product of electrolysis at the anode”.
Using sodium chloride solution, describe an experiment to prove the above statement.
Your answer should include:

(a) Problem statement
(b) Hypothesis
(c) Variables
(d) Materials and apparatus used
(e) Procedure of the experiment
(f) Tabulation of data

The further the distance between two metals in the
electrochemical series, the bigger the potential difference

.
8. You are given the copper strip, lead strip, iron strip, zinc strip, aluminium strip, magnesium strip and
copper(II) sulphate solution.Referring to the statement above, plan a laboratory experiment to construct the
electrochemical series of the potential differences using different pair of metals.

Your explanation should include all the followings:

(a) Aim of the experment
(b) All the variables
(c ) Statement of the hypothesis
(d) List of materials and apparatus
(e) Procedure of the experiment
(f) Tabulation of data

[ 17 marks ]


Chemistry perfect-score-module-form-4-set-3

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