Electrolysis
Electrolysis
Electrolysis
B6 Sodium chloride is used in making many important chemicals including chlorine and hydrogen.
(3)
Total / 10
B8 The NASA space shuttle uses fuel cells to generate electricity. The diagram below shows a
hydrogen-oxygen fuel cell.
external circuit
hydrogen in oxygen in
Na+ (aq)
electrolyte
Water ]
At the positive electrode, oxygen reacts with water as shown.
(
O2(g) + 2H2O(l) + 4e 4OH(aq)
b
At the negative electrode, hydrogen reacts with hydroxide ions as shown.
)
H2(g) + 2OH (aq) 2H2O(l) + 2e
W
The overall reaction in the fuel cell is the reaction between hydrogen and oxygen to make
h
water.
a
(a) Give one source for hydrogen and one source for oxygen for use in a fuel cell. [2]
t
is the name of the electrolyte used in the fuel cell?
[1]
(c) What type of reaction takes place, reduction or oxidation, at the positive electrode?
Explain your answer. [3]
[1]
(d) A fuel cell uses 240 dm3 of hydrogen. Calculate the volume of oxygen needed, and press
the mass of water formed. All gas volumes measured at room temperature and u
r
e
.
[
2
]
electrode reactions for the electrolysis of molten sodium chloride. [
3
Which electrode reaction is an oxidation? Explain your answer. (
e
)
....................................................................................................................................................... D
e
....................................................................................................................................................... s
c
....................................................................................................................................................... ri
b
....................................................................................................................................................... e
(3) s
o
m
(b) Explain why the electrolysis of aqueous sodium chloride using inert electrodes
e
gives hydrogen.
a
d
v
....................................................................................................................................................... a
(1) n
t
(c) Explain the three stages in the purification of water supplies. a
g
e
....................................................................................................................................................... s
a
....................................................................................................................................................... n
d
....................................................................................................................................................... d
(3) is
a
(d) Hydrogen is used to manufacture ammonia, NH3. Calculate the volume of hydrogen d
v
needed to react completely with 240 dm3 a
n
t
a
g
e
s
o
f
u
si
n
g a fuel cell to generate electricity.
[3]
Total / 10
(a) Aqueous copper(II) sulphate contains the following ions, Cu2+, H+, OH and SO42.
Aqueous copper(II) sulphate can be electrolysed using inert electrodes.
cathode Cu2+ + 2e Cu
anode 4OH O2 + 2H2O + 4e
(i) Explain why copper, not hydrogen, is formed at the cathode.
...................................................................................................................................
...................................................................................................................................
(ii) Explain why the formation of oxygen at the anode is an example of oxidation.
...................................................................................................................................
...................................................................................................................................
(iii) The electrolysis of aqueous copper(II) sulphate using copper electrodes has a different
anode reaction.
Give the equation for the electrode reaction at the anode.
................................................................................................................................... [3]
(b) Molten lead(II) bromide decomposes when an electric current is passed through it.
(i) Explain why solid lead(II) bromide will not conduct electricity but molten lead(II)
bromide will.
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
cathode .....................................................................................................................
anode ........................................................................................................................
[4]
Total / 7
IGCSE QUESTIONS SET X (Electrolysis, separation & analysis )
A5 Chlorine, hydrogen and sodium hydroxide are made by the electrolysis of concentrated aqueous
sodium chloride.
(a) Aqueous sodium chloride contains the following ions, Na+, H+, OH and Cl .
Concentrated aqueous sodium chloride can be electrolysed using inert electrodes. The
electrode reactions are represented below.
cathode 2H+ + 2e H2
anode 2Cl Cl 2 + 2e
(i)
purification of water.
..........................................................................................................................................
......................................................................................................................................[1]
..........................................................................................................................................
......................................................................................................................................[1]
...................................................................................................................................
................................................................................................................................... [2]
Total / 8
IGCSE QUESTIONS SET X (Electrolysis)
[3]
+
A5 (a) Concentrated aqueous sodium chloride contains H and OH ions.
(
c
(i) Give the formulae of two other ions present in concentrated aqueous sodium )
chloride. A
l
..............................................................................................................................[1] u
m
(ii) Concentrated aqueous sodium chloride is electrolysed using inert graphite i
electrodes. n
Name the product formed at each electrode. i
u
product at anode ...................................................................................................... m
product at cathode ...............................................................................................[2
Explain why hydrogen, not sodium, is formed at the cathode. is
e
................................................................................................................................... x
tr
a
...................................................................................................................................
c
t
(ii) Suggest why, as the electrolysis proceeds, the concentration of sodium
e
hydroxide in the electrolyte increases.
d
c
................................................................................................................................... o
m
................................................................................................................................... m
[2] e
(b) Describe a chemical test for each of the gases produced during the electrolysis of r
concentrated aqueous sodium chloride. ci
(i) chlorine a
ll
................................................................................................................................... y
fr
................................................................................................................................... o
m
(ii) hydrogen
a
................................................................................................................................... n
a
................................................................................................................................... l
[2] u
m
(c) Describe the use of chlorine in the] i
n
(b) Impure copper can be purified by electrolysis. i
u
Draw a labelled diagram of the electrolytic cell that can be used to purify copper. m
o
r
e
b
y
e
l
e
c
tr
o
ly
sis.
..............................................................................................................................[1]
..............................................................................................................................[1]
[Total: 8]
IGCSE QUESTIONS SET X (Electrolysis and calculation of electrolysis)
(iii) The electrolysis of dilute aqueous sodium chloride liberates oxygen at the anode.
Suggest why the electrolysis of concentrated aqueous sodium chloride liberates
chlorine rather than oxygen.
..................................................................................................................................
.............................................................................................................................. [1]
(b) Aqueous copper(II) sulfate was electrolysed using copper electrodes. The copper anode
lost mass as copper(II) ions were formed and the copper cathode gained mass as copper
atoms were formed.
.............................................................................................................................. [1]
(ii) The results of an experiment involving the electrolysis of aqueous copper(II) sulfate are
shown below
.
Use the information in the table to describe how each of the variables affects the
mass of copper formed at the cathode.
temperature ..............................................................................................................
..................................................................................................................................
current ......................................................................................................................
..................................................................................................................................
time ..........................................................................................................................
.............................................................................................................................. [3]
[Total: 9]
(a) (i) Complete the table, which relates to the electrolysis of different solutions using inert
electrodes
..................................................................................................................................
IGCSE QUESTIONS SET X (Electrolysis)
A1 (a) A student tried to pass an electric current through some solids and liquids.
The six experiments are represented by the diagrams below.
A B C
D E F
...............................................................................................................................[2]
(ii) Give the name of an electrolyte shown in the diagram.
...............................................................................................................................[1]
(iii) In which experiment will oxygen be produced?
...............................................................................................................................[1]
(b) The following diagram represents the electrolysis of molten substance, X.
(i) Label the anode and cathode on the diagram.
...................................................................................................................................
...................................................................................................................................
(iv) Explain why substance X conducts electricity when molten, but not when solid.
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
[5]
Tota
l/9
B9 (a) Brine is an impure solution of sodium chloride. The main impurity in brine is calcium chloride.
It is removed by reacting the brine with sodium carbonate.
...................................................................................................................................
(ii)
.
magnesium X 2.72
magnesium Y 0.78
magnesium Z 1.10
(i) Write an ionic equation, with state symbols, for the reaction which happened.
...................................................................................................................................
(ii) What would you expect to see after the reaction had been taking place for
some time?
...................................................................................................................................
...............................................................................................................................[3]
Total / 5
IGCSE QUESTIONS SET X (Electrolysis)
B10 The diagram shows a cell for purifying copper.
electrolyte
(a) Describe what you would observe during this electrolysis and write the equations for the
reactions at the electrodes. [3]
(i) Explain how the structure of metals allows copper electrodes to conduct electricity. [1]
(ii) Explain why solid copper(II) sulphate does not conduct electricity but an aqueous
solution of copper(II) sulphate does conduct. [2]
(c) Describe how the apparatus shown in the diagram could be modified in order to electroplate an
iron object, such as a knife, with nickel. [2]
(d) Bronze is an alloy of copper and tin. Bronze is less malleable than pure copper. Use ideas about
the structure of metals and alloys to explain why bronze is less malleable than pure copper.
[2]
IGCSE QUESTIONS SET X (Electrolysis)
d.c. power
supply
Construct an ionic equation for the reaction between calcium ions and carbonate ions to produce
calcium carbonate.
...................................................................................................................................
(iii) Suggest how the calcium carbonate is removed from the mixture.
...................................................................................................................................
[3]
(b) Chlorine is manufactured by the electrolysis of concentrated sodium chloride.
...................................................................................................................................
...................................................................................................................................
(ii) Calculate the maximum volume of chlorine, at r.t.p., which can be obtained from 175.5 kg
sodium chloride.
[5]
(c) Chlorine reacts with methane to produce chloromethane, CH3Cl.
Draw a dot and cross diagram to show the bonding in chloromethane.
You only need to show outer (valence) electrons.
[2]
[10 marks]
IGCSE QUESTIONS SET X (Electrolysis)
A5 The diagram shows a cell that can be used to make electrical energy.
voltmeter
V
rod of metal X, Y or Z
magnesium
rod electrolyte
......................................................................................................................................[1]
(b) This table shows the results when rods of three metals, X, Y and Z, are used in separate
experiments.
All the metals are less reactive than magnesium
bulb
LEAD
BROMIDE
TOXIC
heat
[1]
(b) Give two observations expected when the lead bromide is heated to melting point.
1.
2. [2]
(c) State two different safety precautions when carrying out this experiment.
1.
2. [2]
[Total: 6]
(e) An electric current can also be generated by a simple electrochemical cell such as the one shown.
.....
e V .....
.....
.....
magnesium copper .....
.....
.....
.....
.....
.....
.....
electrolyte .....
(magnesium sulphate) .....
.....
.....
.....
.....
.....
(i) Explain why the flow of electrons is in the direction shown in the diagram. .....
.....
(ii) Suggest why silver nitrate would not be a good electrolyte to use in this cell.
.....
.....
.....
.....
IGCSE QUESTIONS SET X (Electrolysis) .....
B7 Copper is purified by the electrolysis of aqueous copper(II) sulfate using copper electrodes. .....
.....
(a) Explain how this process is carried out in the laboratory and give relevant equations for ...
the electrode reactions.
.....
.......................................................................................................................................... .....
.....
.......................................................................................................................................... .....
.....
.......................................................................................................................................... .....
.....
.......................................................................................................................................... .....
.....
.......................................................................................................................................... .....
........................................................................................ (
b
...................................................................................................................................... [4] )
A
q
u
e
o
u
s
c
o
p
p
e
r(
II
)
s
ul
f
a
t
e
c
a
n
al
s
o
b
e
el
e
ct
r
ol
y
s
e
d
u
si
n
g
c
a
r
b
o
n
el
e
ct
r
o
d
e
s.
(i) Write an equation for the reaction which takes place at the anode in this el
electrolysis. e
m
.............................................................................................................................. [1] en
ts.
(ii) Explain why the colour of the copper(II) sulfate solution fades during this
electrolysis. ...........
...........
.................................................................................................................................. ...........
...........
.............................................................................................................................. [1] ...........
...........
(c) Copper is a transition element. ...........
...........
(i) Name two transition elements, or compounds of transition elements, which are ...........
used as catalysts. For each catalyst name an industrial product made using the ...........
catalyst. ...........
.........
..................................................................................................................................
............................................................................................................................
..................................................................................................................................
[
..................................................................................................................................
[Tota
..............................................................................................................................
1
[2]
(ii) Other than acting as catalysts state two properties which are specific to transition
(d) The information below shows the reactivity of chromium, copper and iron with warm
hydrochloric acid.
Least reactive
[1]
A A A
negative electrode electrolyte (aluminium
oxide dissolved
B in molten cryolite)
D
steel case
C
molten aluminium
(a) What information in the diagram shows that aluminium is more dense than the
electrolyte?
[1]
(b) What form of carbon is used for the electrodes in this electrolysis?
[1]
[1]
[1]
[1]
(ii) The oxygen reacts with the carbon anode to form carbon dioxide.
What is the formula of carbon dioxide?
[1]
(iii) Why does the anode decrease in size during electrolysis?
[1]
(f) Each electrolysis cell makes 212 kg of aluminium per day from 400 kg of aluminium oxide.
Calculate how much aluminium can be made from 1 tonne (1000 kg) of aluminium oxide.
[1]
(g) Complete the following sentences about the electrolysis of aluminium oxide using
words from the following list.
[Total: 10]
IGCSE QUESTIONS SET X (Electrolysis & Calculations, Polymer)
chlorine
1. The iron object is cleaned with sulphuric acid, then washed with water.
2. The iron is plated with copper.
3. It is then plated with nickel to prevent corrosion.
4. It is then plated with chromium.
(a) The equation for stage 1 is
Fe + H2SO4 FeSO4 + H2
[2]
(ii) Describe a test for the gas given off in this reaction.
test
result [2]
(b) The diagram shows how iron is electroplated with copper.
_
+
rod of
pure iron object
copper
copper(II) sulphate
solution
(i) Choose a word from the list below which describes the iron object.
Put a ring around the correct answer.
[1]
result
[3]
concentrated
solution of
sodium chloride
graphite anode
and m
mixture of mercury sodiu
mercury cathode recirculated
mercury
sodium chloride
5.6 g
magnesium chloride 1.4 g
magnesium sulphate
1.2 g
water 191.8 g
Calculate the percentage of sodium chloride in this sample of seawater.
[1]
(b) The solution of sodium chloride used for electrolysis is about ten times
more concentrated than in seawater.
State how you could increase the concentration of the salts in seawater.
......................................................................................................................................[1]
(c) What happens to the concentration of the sodium chloride as electrolysis takes place?
......................................................................................................................................[1]
......................................................................................................................................[1]
(e) State one property that graphite must have if it is to be used as an electrode.
......................................................................................................................................[1]
......................................................................................................................................[1]
(g) Sodium is also produced during this electrolysis.
Complete the word equation for the reaction of sodium with water.
35
3
millions of tonnes per year
25
production of chlorine /
20
15
10
0
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990
year
Over which ten year period did chlorine production increase most rapidly?
......................................................................................................................................[1]
H Cl H Cl H Cl H Cl H Cl H Cl H Cl H Cl
C C C C C C C C
+ + +
C C C C C C C C
H H H H H H H H H H H H H H H H
........................................................................................................................................[2]
........................................................................................................................................[1]
Total / 12
IGCSE QUESTIONS SET X (Electrolysis)
positive electrode
+
(graphite)
(a) Suggest
[1]
1 .......................................................................................................................................
2 .......................................................................................................................................
3 ....................................................................................................................................... [3]
Total / 14
IGCSE QUESTIONS SET X (Electrolysis & Calculations, Hydrogen)
6 The electrolysis of a concentrated solution of sodium chloride, provides us with chemicals.
[1]
[1]
[1]
(iii) Name a suitable substance that can be used for the electrodes.
[1]
(c) (i) State the name of the particle which is added to a chlorine atom to make a chloride
ion.
[1]
test
result [2]
(d) If chlorine is allowed to mix with sodium hydroxide, sodium chlorate(I), NaOC1 is formed.
(e) One tonne (1 000 kg) of a commercial solution of sodium hydroxide produced by
electrolysis contains the following masses of compounds.
sodium chloride 10
sodium chlorate(V) 9
water 471
total 1000
(i) How many kilograms of sodium hydroxide will be present in 5 tonnes of the
solution?
[1]
(ii) All the water from one tonne of impure sodium hydroxide is evaporated.
(f) The hydrogen obtained by electrolysis can be used in the manufacture of margarine.
H H H H H H H H
Ni
H C C C C CO2H + H2 H C C C C CO2H
H H H H H H
n n
(i) Complete the following sentences about this reaction using words from
the list.
catal
yst
inhib
itor
mon
omer
ic
satur
ated
unsatu
rated
Hydrogen gas is bubbled through carbon
reaction.
..........................................................................................................................................
......................................................................................................................................[1]
(b) How is the electrolyte of aluminium oxide and cryolite kept molten?
......................................................................................................................................[1]
......................................................................................................................................[1]
..........................................................................................................................................
......................................................................................................................................[2]
(f) During the electrolysis, hot oxygen is formed at the positive electrodes.
Suggest why the positive electrodes have to be replaced frequently.
..........................................................................................................................................
......................................................................................................................................[2]
(g) Aluminium is formed at the negative electrode.
Complete the following equation for the reaction at the negative electrode.
Al3+ + Al
[1]
......................................................................................................................................[1]
[1]
Total / 14
Br Br Br Br
Pb2+ Pb2+
Br Br Br Br
Pb2+ Pb2+
Br Br Br Br
Pb2+ Pb2+
[1]
[2]
A B
electrodes
heat
[1]
(ii) State the name of a metal which can be used for the electrodes.
[1]
(iii) Why does lead bromide have to be molten for electrolysis to occur?
[1]
(iv) State the name of the products formed during this electrolysis;
at the anode,
[1]
(ii) What colour is the solution at the end of the reaction?
[1]
(iii) An aqueous solution of iodine does not react with a solution of sodium bromide.
Explain why there is no reaction.
[1]
(i) Draw the structure of ethene showing all atoms and bonds.
[1]
(ii) Which one of the following, A, B, C or D, shows the correct structure of the product
formed when bromine reacts with ethene?
H Br Br Br H Br Br Br
H C C Br H C C H H C C H H C C H
H H H H H H
A B C D
answer [1]
IGCSE QUESTIONS SET X (Electrolysis)
3 Lead bromide was placed in a tube and connected to an electrical circuit as shown below.
dc power supply
bulb
LEAD
BROMIDE
TOXIC
heat
The lead bromide was heated until molten. A brown gas was given off.
[1]
(c) Name the brown gas. At what electrode will the gas be given off?
name
electrode [2]
2 The diagram shows the apparatus used to find out the effect of an electric current on a
concentrated aqueous solution of sodium chloride.
3 [3]
[1]
(ii) State a test for this product and the result of the test.
test
result [2]
IGCSE QUESTIONS SET X (Electrolysis & Tests)
1 The diagram shows the effect of passing electricity through concentrated hydrochloric acid.
chlorine hydrogen
[1]
test
result [2]
IGCSE QUESTIONS SET X (Electrolysis & Tests)
2 [2]
[1]
(ii) State a test for this product and the result of the test.
test
result [2]
[Total: 6]
IGCSE QUESTIONS SET X (Electrolysis & Test)
6 Concentrated hydrochloric acid was broken down by the passage of electricity using this apparatus.
gas A gas B
concentrat
ed hydrochloric
acid
electrodes
+
..................................................................................................................................... [1]
..................................................................................................................................... [1]
test ..................................................................................................................................
.. result ...........................................................................................................................
[2]
(d) Gas B pops when tested with a lighted splint. What is gas B?
..................................................................................................................................... [1]
[Total: 5]
IGCSE chemistry SET X (Electrolysis & Test)
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.
metal electrode
cup
electrolyte
......................................................................................................................................[1]
......................................................................................................................................[1]
(c) Suggest a suitable electrolyte that could be used to electroplate this cup.
......................................................................................................................................[2]
...............................................................................................................................[1]
...............................................................................................................................[1]
Total / 6
IGCSE chemistry SET X (Electrolysis & Reactivity series)
magnesium
aluminium
zinc
copper
waste gases
[1]
[1]
(iii) Oxygen is produced at the positive electrode (anode). Name another gas which is
given off at this electrode.
[1]
(i) Which of the two metals has the greater tendency to form ions?
[1]
(ii) Describe what you would see when this reaction occurs.
[1]
(c) Complete the following table by writing reaction or no reaction in the spaces provided.
magnesium basic
[2]
aluminium amphoteric
[2]
IGCSE chemistry SET X (Metal, Oxygen & Oxides)
5 (a) Titanium is produced by the reduction of its chloride. This is heated with magnesium in an inert
atmosphere of argon.
[1]
(ii) Name another metal that would reduce titanium chloride to titanium.
[1]
(iii) Suggest how you could separate the metal, titanium, from the soluble salt magnesium
chloride.
[2]
(b) Titanium is very resistant to corrosion. One of its uses is as an electrode in the cathodic
protection of large steel structures from rusting.
power
+
steel oil rig
which is cathode
titanium
anode
sea water contains
H+(aq), OH(aq),
Na+(aq), Cl(aq)
[1]
(ii) The steel oil rig is the cathode. Name the gas formed at this electrode.
[1]
and [2]
[2]
(v) Another way of protecting steel from corrosion is sacrificial protection.
Give two differences between sacrificial protection and cathodic protection.
[2]
[Total: 12]
IGCSE chemistry SET X (Electrolysis)
6 Aluminium is extracted by the electrolysis of a molten mixture that contains alumina, which is aluminium
oxide, Al2O3.
(a) The ore of aluminium is bauxite. This contains alumina, which is amphoteric, and
iron(III) oxide, which is basic. The ore is heated with aqueous sodium hydroxide.
Complete the following sentences.
waste gases
................................
temperature is .........................
[4]
3+ 2-
(c) The ions that are involved in the electrolysis are Al and O .
[2]
[2]
(d) Give an explanation for each of the following.
[1]
[2]
[1]
[Total: 16]
(b) Write an ionic equation for the reaction at the positive electrode (anode).
[2]
in electric wiring,
[2]
in cooking utensils.
[2]
[1]
[Total: 10]
IGCSE chemistry SET X (Electrolysis)
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.
dilute aqueous
sodium chloride
aqueous copper(II)
sulfate
[Total: 8]
10. Mary electrolyses a solution of potassium chloride.
3
The experiment gives off 20 cm of gas in 5 minutes.
......................................................................................................................................................
..................................................................................................................................................[1]
[Total: 1]
IGCSE chemistry SET X (Electrolysis)
......................................................................................................................................................
..................................................................................................................................................[2]
[Total: 2]
9. (a) Potassium chloride is made of ions.
............................................................................................................................................
........................................................................................................................................[2]
............................................................................................................................................
........................................................................................................................................[3]
[Total: 5]
IGCSE chemistry SET X (Electrolysis)
oxygen
hydrogen
-ve + ve
Write down the test she should use and the result she should expect.
test ............................................................................................................................................
result .....................................................................................................................................[2]
anode
anion
cathode
cation
[1] [Total: 3]
IGCSE chemistry SET X (Electrolysis)
+
_
positive electrode
negative electrode
aluminium oxide
liquid aluminium
aluminium
answer ...................................................................................................................................[1]
...............................................................................................................................................[1]
[Total: 2]
X Z
ve + ve
(a) Look at the table. It shows some of the names of the apparatus used.
anode
cathode
test tube
[3]
What are the names of the two gases made during this electrolysis?
carbon dioxide
hydrogen
nitrogen
oxygen
sulfur dioxide
[Total: 5]
IGCSE chemistry SET X (Electrolysis)
12 This question is about electrolysis.
(a) Draw a straight line to match each word with its correct meaning.
word meaning
positive electrode
insulation
negative electrode
electrolyte
tapping hole
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...............................................................................................................................................[3]
[Total: 6]
IGCSE chemistry SET X (Electrolysis)
dc supply
+
Cu2+
H+
OH
SO42
answer ..................................................................................................................................
[1]
(b) Which two of the following observations are correct?
Explain why.
...................................................................................................................................................
...............................................................................................................................................[1]
[Total: 4]
IGCSE chemistry SET X (Electrolysis)
gas Y oxygen
carbon cathode
ve +ve
............................................................................................................................................ [1]
H2O
OH
SO42
[Total:
2]
positive electrode
insulation
negative electrode
electrolyte
tapping hole
(a) Write about how the aluminium is made using this equipment.
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...............................................................................................................................................[3]
(b) There is a higher percentage of aluminium compounds than iron compounds in the Earths
crust.
Explain why.
...............................................................................................................................................[1]
[Total: 4]
IGCSE chemistry SET X (Electrolysis)
dc supply
+
Cu2+
H+
OH
SO42
answer ..................................................................................................................................
[1]
(c) Azhar decides to replace copper(II) sulfate solution with solid copper(II) sulfate.
Explain why.
...................................................................................................................................................
...............................................................................................................................................[1]
[Total: 4]
IGCSE chemistry SET X (Electrolysis)
It shows the apparatus needed for the electrolysis of molten (liquid) lead bromide.
dc power supply
+
molten (liquid)
ceramic crucible lead bromide
heat
Look at the symbol equation. It shows how lead bromide is broken down during electrolysis.
PbBr2 Pb + Br2
.................................................................................................................................... [1]
(ii) Two factors affect how much product is made in this electrolysis.
Write down the other factor that affects how much product is made.
.................................................................................................................................... [1]
(b)
Electrolysis involves the movement of ions.
Molten (liquid) lead bromide can be electrolysed but solid lead bromide cannot.
Explain why.
...................................................................................................................................................
...................................................................................................................................................
............................................................................................................................................ [2]
[Total: 4]
Structured questions:
13.Choose from the words, the term most appropriate for the descriptions below:
Rheostat, battery, ammeter, platinum, voltmeter, copper, cell
a) A source of electricity
1
b) A collection of cells 1
e) An inert electrode 1
14.The table below gives information about four substances, A, B, C and D, when they are
solid and when they are molten.
Solid Molten
Appearance Does the Does the Product at Product at
Substance
solid melt the anode the cathode
conduct? conduct?
A Yellow solid No No None None
B White solid No Yes Bromine Lead metal
C Pink solid Yes Yes gas None
D Black solid Yes Yes None none
None
a) Suggest possible identities for A, B, C and D.
4
b) Is B a conductor, or an electrolyte?
1
c) Is D a conductor, or an electrolyte?
1
15.Draw a simple electrical circuit that you could use if you wished to copper plate a nail.
Name the electrodes you use, indicating which the anode is and which the cathode is. Also
name a suitable electrolyte. 4
16.
Distinguish between Electrolysis and electrolyte
2
Questions
1. Say what is formed at cathode and at the anode during the electrolyses of the following
substances. Assume that carbon electrodes were used each time. You dont need to write
electrode equations.
h) Sodium hydroxide 2
2. Some solid potassium iodide was placed in an evaporating basin. Two carbon electrodes
were inserted and connected to a 12 volt DC power source and a light bulb. The potassium
iodide was heated. As soon as the potassium iodide was molten, the bulb came on. Purple
fumes were seen coming from the positive electrode, and lilac flashes were seen around
the negative one.
a) Explain why the bulb didnt come on until the potassium iodide molted.
3
c) Name the purple fumes seen at the positive electrode, and write the electrode equation
for their formation.
3
d) The lilac flashes seen around the negative electrode are caused by the potassium which
is formed. The potassium burns with a lilac flame. Write the electrode equation for the
formation of the potassium. 2
e) What differences would you expect to observe if you used molten sodium bromide
instead of potassium iodide?
3
f) Write the electrode equations for the reactions occurring during the electrolysis of
molten sodium bromide.
2
3. For each of the following electrolytes (i) write the cathode equation, (ii) write the anode
equation, (iii) say what has been oxidized and what has been reduced.
4.