Topical Hub, IGCSE Chemistry 0620 exam-style questions

Electrochemistry

30 questions: 15 multiple choice, 15 structured.

Download questions (PDF, 241 KB) Back to the topic page Print the mark scheme

1

Core Electrolysis [1]

Which statement is the correct definition of electrolysis?

  1. A The decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current
  2. B The breakdown of a compound using heat energy alone
  3. C The reaction of a metal with an acid to produce a salt and hydrogen
  4. D The process by which a metal ore is converted into the pure metal by heating with carbon

2

Core Electrolysis [1]

Molten zinc chloride is electrolysed using two graphite rods connected to a battery. What is the name given to the positive electrode?

  1. A cathode
  2. B anode
  3. C electrolyte
  4. D terminal

3

Core Electrolysis [1]

Molten lead(II) bromide is electrolysed using inert electrodes. Which pair correctly describes the two products and the electrode at which each forms?

  1. A lead at the anode, bromine at the cathode
  2. B hydrogen at the cathode, oxygen at the anode
  3. C lead at the cathode, bromine at the anode
  4. D lead at the cathode, oxygen at the anode

4

Core Electrolysis [1]

In the electrolysis of any molten ionic compound, which statement is always true?

  1. A A non-metal element is always produced at the cathode
  2. B Two different metals are produced, one at each electrode
  3. C A metal, or hydrogen, is produced at the cathode, and a non-metal other than hydrogen is produced at the anode
  4. D A metal is produced at the anode and a non-metal at the cathode

5

Core Electrolysis [1]

Dilute sulfuric acid is electrolysed using platinum electrodes. What are the products at the cathode and at the anode respectively?

  1. A hydrogen; oxygen
  2. B oxygen; hydrogen
  3. C sulfur; oxygen
  4. D hydrogen; sulfur dioxide

6

Core Electrolysis [6]

Molten lead(II) bromide is electrolysed in a school laboratory using two graphite electrodes connected to a power supply.

(a)

State which electrode – the anode or the cathode – is the negative electrode, and name the product that forms there.

[2]
(b)

State the product that forms at the anode.

[1]
(c)

Describe two observations that would confirm the identity of the product at the anode.

[2]
(d)

State the name of the molten substance that is decomposed in this experiment.

[1]

7

Core Electrolysis [4]

Molten lithium chloride is held in a crucible and electrolysed using two carbon electrodes connected to a d.c. power supply.

(a)

Define the term electrolysis.

[2]
(b)

State the name given to:

(i)

the electrode connected to the negative terminal of the power supply

[1]
(ii)

the molten lithium chloride

[1]

8

Core Electrolysis [1]

Stainless steel cutlery is often electroplated with a thin layer of chromium. What are the main reasons for doing this?

  1. A to improve its appearance and increase its resistance to corrosion
  2. B to make the cutlery lighter and cheaper to produce
  3. C to increase its melting point so it can be sterilised at higher temperatures
  4. D to make the cutlery magnetic

9

Core Electrolysis [5]

A steel spoon is to be electroplated with silver.

(a)

State two reasons why the spoon is electroplated with silver.

[2]
(b)

Describe how the spoon could be electroplated with silver. Your answer should name which electrode the spoon should be, what the other electrode should be made of, and a suitable electrolyte.

[3]

10

Core Electrolysis [1]

Molten calcium bromide is electrolysed using inert electrodes. What are the products formed at the cathode and at the anode respectively?

  1. A bromine; calcium
  2. B calcium; oxygen
  3. C calcium; bromine
  4. D hydrogen; bromine

11

Supplement Electrolysis [1]

Aqueous copper(II) sulfate is electrolysed using two inert carbon electrodes. What is observed at the cathode?

  1. A a colourless gas is released
  2. B a pink/brown solid metal is deposited
  3. C a green solid metal is deposited
  4. D an orange-brown gas is released

12

Supplement Electrolysis [7]

Aqueous copper(II) sulfate is electrolysed twice: once using two inert carbon electrodes, and once, separately, using two copper electrodes.

(a)

State the product formed at the cathode. This is the same in both experiments.

[1]
(b)

With carbon electrodes, state the product formed at the anode.

[1]
(c)

With copper electrodes, describe what happens at the anode instead.

[2]
(d)

Explain why, when copper electrodes are used, the blue colour of the copper(II) sulfate solution stays roughly constant, but with carbon electrodes it gradually fades.

[3]

13

Supplement Electrolysis [1]

Molten sodium chloride is electrolysed using inert electrodes connected to a battery. In the external circuit (the wires connecting the battery to the electrodes), in which direction do electrons flow?

  1. A from the cathode to the anode, through the wires
  2. B electrons do not flow in the external circuit; only ions move
  3. C from the cathode to the anode, through the electrolyte
  4. D from the anode to the cathode, through the wires

14

Supplement Electrolysis [6]

Molten magnesium chloride is electrolysed using inert graphite electrodes connected to a battery.

(a)

Write the ionic half-equation for the reaction at the cathode.

[2]
(b)

Write the ionic half-equation for the reaction at the anode.

[2]
(c)

Describe how charge is carried:

(i)

through the electrolyte

[1]
(ii)

through the external circuit

[1]

15

Supplement Electrolysis [1]

Concentrated aqueous potassium bromide is electrolysed using inert electrodes. What is formed at the anode?

  1. A oxygen
  2. B hydrogen
  3. C bromine
  4. D potassium

16

Supplement Electrolysis [7]

Two separate electrolysis experiments are carried out using inert electrodes: Experiment 1 uses a dilute aqueous solution of sodium iodide; Experiment 2 uses a concentrated aqueous solution of sodium iodide.

(a)

State the product formed at the cathode in both experiments, and explain why sodium metal is not formed there.

[2]
(b)

State the product formed at the anode in Experiment 1 (dilute solution).

[1]
(c)

State the product formed at the anode in Experiment 2 (concentrated solution).

[1]
(d)

Explain, in terms of the ions present, why the anode product is different between the two experiments.

[3]

17

Supplement Electrolysis [1]

Molten potassium chloride is electrolysed using inert electrodes. Which half-equation correctly represents the reaction at the anode?

  1. A K+ + e− → K
  2. B Cl2 + 2e− → 2Cl−
  3. C 2Cl− + 2e− → Cl2
  4. D 2Cl− → Cl2 + 2e−

18

Supplement Electrolysis [6]
(a)

Molten lithium bromide is electrolysed using inert electrodes. Write balanced ionic half-equations for the reactions at:

(i)

the cathode

[1]
(ii)

the anode

[1]
(b)

Dilute sulfuric acid is electrolysed using inert electrodes. Write balanced ionic half-equations, including state symbols, for the reactions at:

(i)

the cathode

[2]
(ii)

the anode

[2]

19

Core Hydrogen–oxygen fuel cells [1]

What is the only chemical product formed when a hydrogen–oxygen fuel cell operates?

  1. A water
  2. B carbon dioxide
  3. C water and carbon dioxide
  4. D hydrogen peroxide

20

Core Hydrogen–oxygen fuel cells [1]

Which two substances react together inside a hydrogen–oxygen fuel cell to generate electricity?

  1. A hydrogen and nitrogen
  2. B hydrogen and oxygen
  3. C methane and oxygen
  4. D hydrogen and carbon dioxide

21

Core Electrolysis [1]

Concentrated aqueous sodium chloride is electrolysed using inert carbon electrodes. What gas is produced at the anode?

  1. A oxygen
  2. B chlorine
  3. C hydrogen
  4. D sodium vapour

22

Core Electrolysis [1]

Molten strontium chloride is electrolysed using inert electrodes. What products form at the cathode and at the anode respectively?

  1. A chlorine; strontium
  2. B strontium; oxygen
  3. C hydrogen; chlorine
  4. D strontium; chlorine

23

Core Electrolysis [5]

Dilute sulfuric acid is electrolysed in the laboratory using platinum electrodes.

(a)

Name the gas produced at the cathode and describe a test that would confirm its identity, including the result.

[2]
(b)

Name the gas produced at the anode and describe a test that would confirm its identity, including the result.

[2]
(c)

State the electrolyte used in this experiment.

[1]

24

Core Electrolysis [5]

A car bumper made of steel is electroplated with a thin layer of chromium before sale.

(a)

State two reasons why the bumper is electroplated with chromium rather than left as bare steel.

[2]
(b)

Describe how the bumper could be electroplated with chromium. Your answer should name which electrode the bumper should be, a suitable material for the other electrode, and a suitable electrolyte.

[3]

25

Supplement Electrolysis [8]

Impure copper is purified using electrolysis. A block of impure copper is used as the anode and a thin strip of pure copper as the cathode. Both are dipped into aqueous copper(II) sulfate.

(a)

Write the ionic half-equation for the reaction at the cathode.

[2]
(b)

Write the ionic half-equation for the reaction at the anode.

[2]
(c)

Explain what happens to the mass of the anode and the mass of the cathode as electrolysis proceeds.

[2]
(d)

Explain why the concentration of the copper(II) sulfate solution stays approximately constant during this process.

[2]

26

Supplement Electrolysis [8]

In industry, concentrated aqueous sodium chloride (brine) is electrolysed continuously using inert electrodes. This is called the chlor-alkali process.

(a)

State the products formed at the cathode and at the anode.

[2]
(b)

Write the ionic half-equation for the reaction at the anode.

[2]
(c)

Name the solution that remains after electrolysis, and state one industrial use of it.

[2]
(d)

Explain, in terms of the ions present, why chlorine rather than oxygen is formed at the anode, even though oxygen is normally the preferred product at a carbon anode in dilute aqueous solution.

[2]

27

Supplement Electrolysis [5]

Dilute sulfuric acid is electrolysed using inert platinum electrodes connected to a battery.

(a)

Describe how charge is carried through the dilute sulfuric acid (the electrolyte).

[2]
(b)

Describe how charge is carried through the wires of the external circuit.

[1]
(c)

State what happens to hydrogen ions when they reach the cathode.

[2]

28

Core Hydrogen–oxygen fuel cells [4]

A hydrogen–oxygen fuel cell is used to power the electric motor of an experimental car.

(a)

State the two gases that are supplied to the fuel cell.

[1]
(b)

State the only chemical product of the fuel cell reaction, and explain why the car's exhaust does not release carbon dioxide, unlike a petrol-engine car.

[3]

29

Supplement Hydrogen–oxygen fuel cells [6]
(a)

State two advantages of using a hydrogen–oxygen fuel cell, rather than a petrol engine, to power a vehicle.

[2]
(b)

State two disadvantages of using a hydrogen–oxygen fuel cell, rather than a petrol engine, to power a vehicle.

[2]
(c)

Suggest one reason why hydrogen fuel cell vehicles are not yet as widely used as petrol-engine vehicles.

[2]

30

Supplement Hydrogen–oxygen fuel cells [6]

A car manufacturer advertises its hydrogen fuel cell car as "100% pollution-free, with zero emissions."

(a)

Explain why this claim is accurate in terms of what comes out of the car's exhaust while it is being driven.

[2]
(b)

Evaluate whether the claim that the car is "100% pollution-free" is a fair description of its overall environmental impact, considering how the hydrogen fuel might be produced.

[4]