IGCSE Grade (10)

Topic 6

Electricity and chemistry

• Electrolysis

• Applications of electrolysis
IGCSE Grade (10)

Paper 2

Question Answer Question Answer

1 B 21 D
2 D 22 D
3 A 23 D
4 D 24 D
5 C 25 B
6 D 26 C
7 A 27 B
8 B 28 D
9 B 29 C
10 C 30 D
11 D 31 B
12 C 32 A
13 A 33 A
14 A 34 B
15 B 35 B
16 C 36 C
17 A 37 D
18 B 38 B
19 B 39 A
20 B 40 A
IGCSE Grade (10)

Paper 4
1. J. 02 (1. b)
(b) Aluminium is produced by the electrolysis of an electrolyte that contains aluminium
oxide.

(i) Write an ionic equation for the reduction of the aluminium ion at the cathode.

Al3+ + 3 e- .. Al [2]

(ii) Name the main ore of aluminium.

Bauxite ..[1]

(ii) Complete the following description of the electrolyte by filling the spaces.

The electrolyte is a ............molten.................... mixture of aluminium oxide

and ...........cryolite...................... which is maintained at 900 °C. [2]

(iv) Explain why the gas given off at the anode is a mixture of oxygen and carbon
dioxide.

Oxygen from oxide formed at anode, then reacts at high temperature with carbon to
form carbon dioxide gas that escapes.. [2]

2. N. 02 (4. b, c)
(b) Copper is refined by the electrolysis of aqueous copper (II) sulfate using copper
electrodes. Describe the change that occurs at the electrodes.

(i) cathode (pure copper) ...mass increases as copper deposits ...........................

...[1]

(ii) anode (impure copper) mass decreases as copper is ionized and goes to the
solution [1]
IGCSE Grade (10)
(iii) Write an ionic equation for the reaction at the cathode.

Cu2+ + 2 e- ... Cu .[1]

(iv) If carbon electrodes are used, a colourless gas is given off at the anode and the
electrolyte changes from a blue to a colourless solution.

The colourless gas is . Oxygen.

The solution changes into Sulfuric acid. [2]

(c) Electrolysis and cells both involve chemical reactions and electricity.

What is the essential difference between them?

Cells change chemical energy to electric energy

Electrolysis changes electric energy to chemical energy. [2]

3. J. 03 (1. e)
(e) One of the methods used to prevent iron or steel from rusting is to electroplate it with
another metal, such as tin. Complete the following.

The anode is made of Tin

The cathode is made of Iron / steel

The electrolyte is a solution of . Tin salt solution .

[3]

4. J. 03 (5. b)
(b) All three metals can be obtained by the electrolysis of a molten halide. The electrolysis
of the aqueous halides does not produce the metal.

(i) Complete the equation for the reduction of lanthanum ions at the negative
electrode (cathode).

La3+ + ......3 e -....... ......La..

(iii) Name the three products formed by the electrolysis of aqueous caesium bromide.

Hydrogen + Bromine + Caesium hydroxide

IGCSE Grade (10)
[4]

5. J. 04 (5. b, c)
(b) Aqueous copper(II) sulfate solution can be electrolyzed using carbon electrodes.
The ions present in the solution are as follows

Cu2+(aq) , SO42– (aq), H+(aq), OH– (aq)

(i) Write an ionic equation for the reaction at the negative electrode (cathode).

Cu2+ + 2 e- Cu …[1]

(ii) A colourless gas was given off at the positive electrode (anode) and the solution
changes from blue to colourless.

Explain these observations.

Oxygen gas evolved at anode. Blue Aqueous copper sulfate is changed to

colourless sulfuric acid / copper ions are discharged [2]

(c) Aqueous copper(II) sulfate can be electrolyzed using copper electrodes. The
reaction at the negative electrode is the same but the positive electrode becomes
smaller and the solution remains blue.

(i) Write a word equation for the reaction at the positive electrode.

Copper - 2 electrons Copper II ions .[1]

(ii) Explain why the colour of the solution does not change.

Concentration of copper ions is kept constant .[2]

(iii) What is the large scale use of this electrolysis?

…………………Purification of copper………………………..……………………..[1]
IGCSE Grade (10)

6. J. 05 (6. a)
The position of aluminium in the reactivity series of metals is shown below.

magnesium
aluminium
zinc
copper

(a) Aluminium is extracted by the electrolysis of its molten oxide.

(i) Name the main ore of aluminium.

…………………………………Bauxite …………………………………………………….[1]

(ii) Why does the molten electrolyte contain cryolite?

To reduce melting point of Al2O3 saves energy and improve electrical conductivity.[1]

(iii) Oxygen is produced at the positive electrode (anode). Name another gas which is
given off at this electrode.

…………………Carbon dioxide…………………………..…………………………….[1]

7. N. 05 (5. c)
(c) The major ore of strontium is its carbonate, SrCO3. Strontium is extracted by the
IGCSE Grade (10)
electrolysis of its molten chloride.

(i) Name the reagent that will react with the carbonate to form the chloride.

……………………Hydrochloric acid………………….…………………………………[1]
(ii) The electrolysis of molten strontium chloride produces strontium metal and
chlorine. Write ionic equations for the reactions at the electrodes.

negative electrode (cathode) Sr2+ + 2 e- Sr

positive electrode (anode)………… 2 Cl1- - 2 e- Cl2 [2]

(iii) One of the products of the electrolysis of concentrated aqueous strontium chloride
is chlorine. Name the other two.

Hydrogen and strontium hydroxide

…[2]

8. N.06 (6. b)
(b) Impure copper is extracted from the ore. This copper is refined by
electrolysis.

(i) Name :

the material used for the positive electrode (anode),…Impure copper …….

the material used for the negative electrode (cathode),……Pure copper………..….

a suitable electrolyte……Copper sulfate solution / Cu2+ …………..………[3]

(ii) Write an ionic equation for the reaction at the negative electrode.

…… ……… Cu2+ + 2 e- Cu ……….[1]

(iv) One use of this pure copper is electrical conductors, another is to make alloys.

Name the metal that is alloyed with copper to make brass.

……………………………Zinc ……………………………………………..…….[1]
IGCSE Grade (10)
9. J. 07 (6. b, c)
(b) Complete the labelling of the diagram.

(c) The ions that are involved in the electrolysis are Al3+ and O2-.

(i) Write an equation for the reaction at the cathode.

……… Al3+ + ...3 e -....... ......Al .[2]

(ii) Explain how carbon dioxide is formed at the anode.

Oxygen gas evolved at anode. Blue Aqueous copper sulfate is changed to

colourless sulfuric acid / copper ions are discharged … .[2]

10. N. 07 (4. c)
(d) The remaining zinc oxide reacts with sulfuric acid to give aqueous zinc
sulfate.

This is electrolysed with inert electrodes (the electrolysis is the same as that of is
electrolysed with inert electrodes (the electrolysis is the same as that of copper(II)
sulfate with inert electrodes) ions present:

Zn2+(aq) SO42-(aq) H+(aq) OH-(aq)

(i) Zinc forms at the negative electrode (cathode). Write the equation for this
reaction.

Zn2+ + ...2e -....... .....Zn .[1]

IGCSE Grade (10)

(ii) Write the equation for the reaction at the positive electrode (anode).

4 OH- - 4e O2 + 2 H2O

[2]

(iii) The electrolyte changes from aqueous zinc sulfate to

……………Sulfuric acid………………………..…………………..[1]

(e) Give two uses of zinc.

1……Prevents iron from rusting by galvanization

2……making alloys [brass] / coining / roofing ….………………………..…….. [2]

11. J. 08 ( 3. a)
Copper is purified by electrolysis.

(a) Complete the following.

The positive electrode (anode) is made from impure copper

The negative electrode (cathode) is made from…………pure copper …..………...

The electrolyte is aqueous………………Copper sulfate solution …………… [3]

(b) Write an ionic equation for the reaction at the positive electrode (anode).

Cu2+ + 2 e- Cu
..[2]

12. N. 08 (5. a)
The electrolysis of concentrated aqueous sodium chloride produces three commercially
important chemicals; hydrogen, chlorine and sodium hydroxide.

(a) The ions present are Na+(aq), H+(aq) Cl–(aq) and OH–(aq).

(i) Complete the ionic equation for the reaction at the negative electrode (cathode).

………2H+…….. + ……2e-……. H2 [1]

IGCSE Grade (10)
(ii) Complete the ionic equation for the reaction at the positive electrode (anode).

2Cl – − ……2e-……. ………Cl2…….. [1]

(iii) Explain why the solution changes from sodium chloride to sodium hydroxide.

Sodium ions and hydroxide ions are left ….[1]

13. J. 09 (2)
The results of experiments on electrolysis using inert electrodes are given in the table.

Complete the table; the first line has been completed as an example.

Molten
potassium iodide

Water used up /
Hydrogen Oxygen sodium chloride
is left

Copper Oxygen Sulfuric acid is

left

Aqueous
potassium
Bromide
IGCSE Grade (10)
14. J. 2010 (32) [7]
Aluminium was fi rst isolated in 1827 using sodium.
AlCl3 + 3Na → Al + 3NaCl
Aluminium, obtained by this method, was more expensive than gold.
(a) Suggest an explanation why aluminium was so expensive.
sodium is expensive , hard to extract and high energy costs in its
extraction from sodium chloride [1]

(b) The modern method for extracting aluminium is the electrolysis of a molten electrolyte,
aluminium oxide dissolved in cryolite. The aluminium oxide decomposes.
2Al 2O3 → 4Al + 3O2
Both electrodes are made of carbon.
(i) Give two reasons why the oxide is dissolved in cryolite.
reduces melting point of Aluminium oxide / provides better
conductivity / Saves energy [2]
(ii) Complete the ionic equation for the reaction at the anode.
....2... O2– → O2 + ....4... e– [2]

(iii) Why do the carbon anodes need to be replaced frequently?

they burn react with oxygen from aluminium oxide , forming carbon
dioxide gas [1]

(c) The electrolysis of a molten electrolyte is one method of extracting a metal from its ore.
Other methods are the electrolysis of an aqueous solution and the reduction of the
oxide by carbon. Explain why these last two methods cannot be used to extract

Aluminium electrolysis of an aqueous solution Hydrogen formed in preference to

Al as H+ is more reactive than Al3+

Using carbon Aluminium is more reactive than carbon so carbon cannot

reduce aluminium oxide [2]

[Total: 8]
IGCSE Grade (10)
15. N. 2010 (32) [4, b]
(b) Chromium is used to electroplate steel objects. The diagram shows how this could be
done.

(i) Give two reasons why steel objects are plated with chromium.
Good shiny appearance / resist corrosion [2]

(ii) The formula of the chromium (III) ion is Cr3+ and of the sulfate ion is SO42–. Give the
formula of chromium (III) sulfate.
……………............................. Cr2(SO4)3.............................................................................. [1]

(iii) Write the equation for the reaction at the negative electrode (cathode).
………….............. Cr3+ + 3e → Cr.................................................. [2]

(iv) A colourless gas, which relights a glowing splint, is formed at the positive electrode
(anode). Name this gas.
……………............................Oxygen.................................................................................. [1]

(v) During electrolysis, it is necessary to add more chromium (III) sulfate but during copper-
plating using a copper anode, it is not necessary to add more copper(II) sulfate. Explain.

to replace chromium ions (used to plate steel) as copper ions replaced

from copper anode [2]
IGCSE Grade (10)
16. N. 2010 (33) [4]
The electrolysis of concentrated aqueous sodium chloride, between inert electrodes, is used
to make four important chemicals.
Hydrogen
Chlorine
Sodium hydroxide
Sodium chlorate (I)
(a) The ions present in the electrolyte are Na+, H+, Cl – and OH –.

(i) Hydrogen ions are discharged at the negative electrode (cathode).

Write an equation for this reaction.
2H+ + 2e- H2 [2]

(ii) The hydrogen ions are from the water.

Suggest an explanation why the concentration of hydroxide ions increases.

H+ are discharged / reduced / more water molecules ionized to replace
hydrogen ions
[2]

(iii) When a dilute solution of sodium chloride is used, chlorine is not formed at the
positive electrode (anode), a different gas is produced. Name this gas.
.............................................Oxygen.................................................................... [1]

(iv) State an example of an inert electrode.

….................................Carbon / graphite......................................................... [1]

(b) (i) State a use of hydrogen.

……….......................................Rocket fuel.......................................................... [1]
IGCSE Grade (10)
17. N. 2011 (31) [3]

Aluminium is extracted by the electrolysis of a molten mixture of alumina, which is aluminium

oxide, and cryolite.

(a) (i) Alumina is obtained from the main ore of aluminium.

Name this ore.
…….....................................................Bauxite............................................................. [1]

(ii) Explain why it is necessary to use a mixture, alumina and cryolite, rather than just
alumina.
reduces melting point of Aluminium oxide / provides better
conductivity / Saves energy [2]

(iii) Copper can be extracted by the electrolysis of an aqueous solution.

Suggest why the electrolysis of an aqueous solution cannot be used to extract aluminium.
Copper formed in preference to H2 as Cu2+ is more reactive than H+
Hydrogen formed in preference to Al as H+ is more reactive than Al3+
[2]
IGCSE Grade (10)
(b) The ions which are involved in the electrolysis are Al 3+ and O2–. The products of this
electrolysis are given on the diagram.
Explain how they are formed. Use equations where appropriate.
Al3+ + 3e- → Al Aluminium ion is reduced
2O2– → O2 + 4e- oxide ion is oxidized
oxygen reacts with carbon (anode) to form carbon dioxide
C + O2 → CO2 [4]

(c) The uses of a metal are determined by its properties.

(i) Foods which are acidic can be supplied in aluminium containers.

Explain why the acid in the food does not react with the aluminium.
Due to protective oxide layer [1]

(ii) Explain why overhead electrical power cables are made from aluminium with a steel core.

Aluminium has low density and is a good conductor of electricity

core made of steel to strengthen the cable and prevents sagging
[3]
[Total: 13]
IGCSE Grade (10)
18. J. 2012 (32) [4]
The ore of aluminium is bauxite which is impure aluminium oxide. Alumina, pure aluminium
oxide, is obtained from bauxite.
Aluminium is formed at the cathode when a molten mixture of alumina and cryolite, Na3AlF6,
is electrolyzed.

(a) (i) Name two products formed at the anode in this electrolysis.
Oxygen/ carbon dioxide / fluorine / carbon monoxide [2]

(ii) All the aluminium formed comes from the alumina not the cryolite.
Suggest two reasons why the electrolyte must contain cryolite.
reduces melting point of Aluminium oxide / provides better
conductivity / Saves energy. [2]

(iii) The major impurity in bauxite is iron (III) oxide. Iron (III) oxide is basic, aluminium
oxide is amphoteric. Explain how aqueous sodium hydroxide can be used to
separate them.
Al2O3 reacts with sodium hydroxide forming a water soluble salt and
water while Fe2O3 does not, and removed by filtration [2]

(b) The purification of bauxite uses large amounts of sodium hydroxide.

(i) Describe the chemistry of how sodium hydroxide is made from concentrated aqueous
sodium chloride. The description must include at least one ionic equation.
By electrolysis and aqueous sodium chloride is the electrolyte with
graphite electrodes
Chlorine formed at anode 2Cl– - 2e- → Cl2
Hydrogen formed at cathode 2H+ + 2e- → H2
NaOH / sodium hydroxide solution is left behind [5]
IGCSE Grade (10)
(ii) Making sodium hydroxide from sodium chloride produces two other chemicals.
Name these two chemicals and state one use of each chemical.

Chemical......................................Hydrogen ..............................................

Use...................................................Fuel...........................................................

Chemical.......................................Chlorine.........................................................

Use........................................Water treatment........... ...................................... [2]

[Total: 13]
19. N. 2012 (32) [6]

During electrolysis, ions move in the electrolyte and electrons move in the external circuit.
Reactions occur at the electrodes.
(a) The diagram shows the electrolysis of molten lithium iodide.

(i) Draw an arrow on the diagram to show the direction of the electron flow in the external
circuit. [1]

(ii) Electrons are supplied to the external circuit. How and where is this done?
From negative electrode of battery to external circuit;
And from anode where negative iodide ions lose electron [2]
IGCSE Grade (10)
(iii) Explain why solid lithium iodide does not conduct electricity but when molten it is a
good conductor.
Ionic compound, ions are stuck in lattice, no freely moving ions [1]

(b) The results of experiments on electrolysis are shown in the following table. Complete
the table. The first line has been done as an example.

Copper Sulfuric acid

Hydroge Potassium hydroxide

(c) The diagram below shows the electrolysis of dilute sulfuric acid. Hydrogen is formed at the
negative electrode (cathode) and oxygen at the positive electrode (anode) and the
concentration of sulfuric acid increases.

The ions present in the dilute acid are H+(aq), OH–(aq) and SO42–(aq).
(i) Write an equation for the reaction at the negative electrode (cathode).
......................... 2H+ + 2e- H2.................................................. [2]
(ii) Complete the equation for the reaction at the positive electrode (anode).
4OH–(aq) → O2 (g) +.2.H2O (l) + 4e- [1]

(iii) Suggest an explanation of why the concentration of the sulfuric acid increases.
...................................... water used up................................................... [1]
IGCSE Grade (10)

Paper 6
1. N. 01 (2)
A metal cup can be coated in silver by electrolysis. The cup must be very clean and also
rotated during the process, which is known as electroplating.

(a) Should the metal cup be the anode or the cathode?

...............................................Cathode. ......................................................[1]

(b) Identify the metal from which the electrode is made.

...............................................Silver. ..............................................................................[1]

(c) Suggest a suitable electrolyte that could be used to electroplate this cup.

........................Silver nitrate solution.. ....................................................[2]

(d) Suggest why the cup must be

(i) very clean, ..............Silver can stick ..................................

......................................................................................................................................... .[1]
IGCSE Grade (10)
(ii) rotated during the electrolysis. ..................................................................................

................to be plated from all directions / evenly coated........................................[1]

2. J. 05 (2)
The diagram shows the apparatus used to find out the effect of an electric current on a
concentrated aqueous solution of sodium chloride.

(a) On the diagram label the electrodes [1]

(c) Give three observations when the circuit is switched on.

1 the bulb gets out light

2 colourless bubbles at cathode

3 yellowish green bubbles at anode [3]

(d) (i) Name the product at the positive electrode (anode).

……………………………Chlorine …………………………………………………………..[1]
IGCSE Grade (10)
3. N. 05 (2. a, b)
The diagram shows the apparatus used to pass an electric current through concentrated
hydrochloric acid.

(a) Label the electrodes. [1]

Indicated to square parts

(b) Give two observations when the current is switched on.

1…………… the bulb gets out light ………

2 colourless bubbles at cathode

/ Yellowish green bubbles at anode.. [2]

IGCSE Grade (10)
4. J. 08 (2)
The diagram shows an experiment to pass electricity through lead bromide.

Electricity has no effect on solid lead bromide.

(a) (i) Clearly label the electrodes on the diagram.

Indicated to the parts inside the tube [1]

(iii) Suggest a suitable material to make the electrodes.

…………………………graphite……………………………………………………………. [1]

(b) Give two observations expected when the lead bromide is heated to melting point.

1 Grey deposit at cathode

2 reddish brown colour at anode. [2]

(c) State two different safety precautions when carrying out this experiment.

1………………Fume cupboard ……………………………………………….

2………………Gloves / eye goggles ………………………………………….. [2]

IGCSE Grade (10)
Nov. 2010 (6)
5.

Bubble
s

Alkali formed

Chlorine

The colour bleached

 IGCSE Grade (10)
Nov. 2012 (2)
6.

Graphite

Negative / Cathode

Using distilled water

Hairdryer / heat
 IGCSE Grade (10)
J. 2013 (1)
7.

Electrodes

Light bulb

Lighted splint
Pop sound

Measuring cylinder / Filled with Conc. hydrochloric acid

Sodium hydroxide
IGCSE Grade (10)
J. 2015 (2)
8.

Bulb lights / Silvery gray sold / bubbles

Graphite

It reacts

Bromine

Bleaches

Lead

Fume cupboard