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Extraction of metals
Model Answers 1
Level
IGCSE
Subject
Chemistry (0620/0971)
Exam Board
Cambridge International Examinations (CIE)
Topic
Metals
Sub-Topic
Extraction of metals
Booklet
Model Answers 1
Time Allowed:
48 minutes
Score:
/40
Percentage:
/100
Grade Boundaries:
1
9
8
7
6
5
4
3
2
1
>85%
75%
68%
60%
53%
48%
40%
33%
<25%
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1. In a blast furnace, iron(III) oxide is converted to iron and carbon monoxide is converted to carbon
dioxide.
Fe2O3 + 3CO → 2Fe + 3CO2
What happens to each of these reactants?
A
Both iron(III) oxide and carbon monoxide are oxidised.
B
Both iron(III) oxide and carbon monoxide are reduced.
C
Iron(III) oxide is oxidised and carbon monoxide is reduced.
D
Iron(III) oxide is reduced and carbon monoxide is oxidised.
●
The iron(III) oxide is reduced as it loses oxygen:
○
●
The carbon monoxide is oxidised as it gains oxygen:
○
●
2
Fe2O3 → 2Fe
3CO → 3CO2
A, B and C are therefore incorrect.
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2. Some metals react readily with dilute hydrochloric acid.
Some metals can be extracted by heating their oxides with carbon.
For which metal are both statements correct?
A
calcium
B
copper
C
iron
D
magnesium
 A and D are incorrect as calcium and magnesium are too reactive and need to be
extracted by electrolysis.
 B is incorrect as copper is very low down on the reactivity series and does not react with
dilute HCl.
4
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3. The diagram shows the materials used in the production of steel from impure iron.
impure
iron
oxygen
an oxide of element X
steel
What could element X be?
A
calcium
B
carbon
C
nitrogen
D
sulfur
 Steel is made by purifying iron made in the blast furnace.
 Impure iron or “pig iron” contains impurities of carbon, phosphorus, silicon and sulfur.
 It is placed in a vessel called a basic oxygen converter and oxygen is blown in to oxidise
the impurities to their oxides, which are then removed.
 The removal is done by reaction with calcium oxide, which produces slag:
○
SiO2 + CaO → CaSiO3
 The slag floats on the molten iron and is removed.
 B and D are incorrect as carbon and sulfur are impurities which are removed during the
process, not added.
 D is incorrect as nitrogen is not used in this process
5
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Basic oxygen converter
6
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4. The diagram shows the manufacture of steel.
gas X
waste gases
molten iron
What is gas X?
A
carbon dioxide
B
chlorine
C
hydrogen
D
oxygen
 Steel is produced by first purifying iron which occurs in the blast furnace where the iron
is heated to a temperature in excess of 900ºC.
 It is placed in a vessel called a basic oxygen converter that blows oxygen in to oxidise
the impurities to their oxides, so gas X is oxygen.
 Calcium oxide is added to remove the silicon and phosphorus by reacting with their
oxides producing slag which is then removed.
 A is incorrect as carbon dioxide is a waste gas which is removed.
 B and C are incorrect as these gases are not involved in the process.
7
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Basic oxygen converter
8
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5. A metal is extracted from hematite, its oxide ore.
What is the metal and how is the oxide reduced?
metal
method of reduction
A
Al
electrolysis
B
Al
heating with carbon
C
Fe
electrolysis
D
Fe
heating with carbon
 Hematite is the mineral ore of iron, which is found as iron (III) oxide, Fe2O3.
 Iron is below carbon on the reactivity series and thus can be removed from the ore by
heating with carbon in a blast furnace.
 A and B are incorrect as aluminium is found in bauxite.
 C is incorrect as iron is not extracted by electrolysis as it is not above carbon in the
reactivity series.
Extraction methods
9
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6. Which row describes the conditions used to make steel from the iron produced by a blast
furnace?
 Steel alloys are produced by first purifying iron and then adding small amounts of
different elements such as nickel or chromium, depending on the alloy being made.
 Purifying iron occurs in the blast furnace where the iron is heated to a temperature in
excess of 900ºC.
 Impure iron or “pig iron” contains impurities of carbon, phosphorus, silicon and sulfur.
 It is placed in a vessel called a basic oxygen converter that blows oxygen in to oxidise
the impurities to their oxides.
 Calcium oxide is added to remove the silicon and phosphorus by reacting with their
oxides producing slag which is then removed.
 B, C and D are incorrect as all three conditions are required in the process.
10
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Basic oxygen converter
11
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7. The Basic Oxygen Process converts iron into steel.
In step 1, oxygen is blown into impure molten iron.
In step 2, oxides are removed by reaction with calcium oxide.
oxygen
waste
gases
molten iron
and
calcium oxide
Which chemical reaction takes place in step 1 and which type of oxides are removed in step 2?
chemical reaction
in step 1
type of oxides removed
in step 2
A
carbon is converted to carbon dioxide
acidic
B
carbon is converted to carbon dioxide
basic
C
iron is converted to iron(III) oxide
acidic
D
iron is converted to iron(III) oxide
basic
 Steel is made by purifying iron made in the blast furnace.
 Impure iron or “pig iron” contains impurities of carbon, phosphorus, silicon and sulfur.
12
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 It is placed in a vessel called a basic oxygen converter and oxygen is blown in to
oxidise the impurities to their oxides.
 In step 1 carbon reacts with oxygen and heats up the blast furnace, forming carbon
dioxide:
• C + O2 → CO2
 In step 2 calcium oxide removes the silicon and phosphorus impurities by reacting with
their acidic oxides producing slag:
• SiO2 + CaO → CaSiO3
 The slag floats on the molten iron and is removed.
 B is incorrect as silicon and phosphorus are nonmetal elements and form acidic oxides.
 C and D are incorrect as carbon monoxide reduces the iron(III) oxide in the iron ore to
form iron:
• Fe2O3 + 3CO → 2Fe + 3CO2
 Iron is the desired product and so is not converted to iron(III) oxide in the process.
13
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8. Iron is extracted from its ore in a Blast Furnace.
Hematite, coke, limestone and hot air are added to the furnace.
Which explanation is not correct?
A
Coke burns and produces a high temperature.
B
Hematite is the ore containing the iron as iron oxide.
C
Hot air provides the oxygen for the burning.
D
Limestone reduces the iron oxide to iron.
 Statement A is correct as coke reacts with oxygen and heats up the blast furnace,
forming carbon dioxide:
• C + O2 → CO2
 Statement B is correct as the main iron ore is hematite, Fe2O3.
 Statement C is correct as hot air is blasted in to provide oxygen for the carbon to burn.
 Statement D is incorrect as carbon monoxide reduces the iron(III) oxide in the iron ore
to form iron:
• Fe2O3 + 3CO → 2Fe + 3CO2
 Limestone is added to produce calcium oxide which removes silicon and phosphorus
impurities by reacting with their acidic oxides producing slag:
• SiO2 + CaO → CaSiO3
 The slag floats on the molten iron and is removed.
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9. Which statement about the extraction of iron from its ore is correct?
A
Iron is more difficult to extract than zinc.
B
Iron is more difficult to extract than copper.
C
Iron is easy to extract because it is a transition metal.
D
Iron cannot be extracted by reduction with carbon.
 The ease with which a metal can be extracted from its ore depends on the metals
position on the reactivity series.
 Metals lower down on the series can be extracted by heating them with carbon which
reduces the metal by removing the oxygen from its oxide.
 Metals that are placed higher up on the series need to be extracted using electrolysis
as these metals are so reactive that their oxides cannot be reduced by carbon.
 Metals that are close together such as zinc and iron are both reduced by carbon, but
since zinc is more reactive it forms a more stable oxide.
 This means that more energy is required to extract zinc than iron, hence it is more
difficult and expensive to extract.
 Iron is higher up on the reactivity series than copper, it´s oxide is more stable and thus
is more difficult to extract than copper which is a relatively unreactive metal.
 A is incorrect as iron is below zinc and so is easier to extract.
 C is incorrect as iron is a transition element but this has no effect on the method used or
difficulty in its extraction.
 D is incorrect as iron is extracted by reduction with carbon in a blast furnace.
15
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Metal extraction methods
16
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10. Many metals are extracted from their ores by heating the metal oxide with carbon.
Which metal cannot be extracted using this method?
A
aluminium
B
copper
C
iron
D
zinc
 The method used to extract a metal from its ore depends on the metals position on the
reactivity series.
 Metals lower down on the series can be extracted by heating them with carbon which
reduces the metal by removing the oxygen from its oxide.
 Metals that are placed higher up on the series need to be extracted using electrolysis
as these metals are so reactive that their oxides cannot be reduced by carbon.
 Metal A, aluminium is too high up on the series and cannot be reduced by carbon, so it
can only be extracted by electrolysis.
 B, C and D are incorrect as copper, iron and zinc are relatively unreactive metals and
can be extracted by heating the oxide with carbon.
Metal extraction methods
17
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11 Iron is extracted from hematite in the Blast Furnace.
waste gases
raw materials
firebrick lining
air
slag
molten iron
The hematite contains silica as an impurity.
What reacts with this impurity to remove it?
18
A
calcium oxide
B
carbon
C
carbon dioxide
D
oxygen
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 Impure iron or “pig iron” contains impurities of carbon, phosphorus, silicon and sulfur.
 Oxygen is blown in to oxidise the impurities to their oxides.
 Calcium oxide is added to remove the silicon and phosphorus by reacting with their
oxides producing slag:
○
SiO2 + CaO → CaSiO3
 The slag floats on the molten iron and is removed.
 B is incorrect as carbon reacts with oxygen and heats up the blast furnace, forming
carbon dioxide:
○
C + O2 → CO2
 C is incorrect as the CO2 formed in the previous equation reacts with carbon to form
carbon monoxide which is the reducing agent:
○
CO2 + C → 2CO
 D is incorrect as oxygen reacts with carbon to heat up the furnace at the beginning of
the process.
Blast furnace
19
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12. Which substance is not involved in the extraction of iron from hematite?
A
carbon
B
carbon monoxide
C
calcium carbonate
D
nitrogen
 Nitrogen is not used in the extraction of iron.
 A, B and C are involved in the process.
 Carbon reacts with oxygen and heats up the blast furnace, forming carbon dioxide:
•
C + O2 → CO2
 Calcium carbonate decomposes to form CO2 and CaO which removes slag:
•
CaCO3 → CO2 + CaO
 The CO2 formed in the above two equations reacts with carbon to form carbon
monoxide which is the reducing agent:
•
CO2 + C → 2CO
 Carbon monoxide reduces the Iron (III) oxide in the iron ore to form iron:
•
20
Fe2O3 + 3CO → 2Fe + 3CO2
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13. Which statement is incorrect?
A
Carbon dioxide is a waste product in the extraction of iron.
B
Carbon monoxide is a reducing agent.
C
The extraction of iron from hematite involves reduction.
D
When iron is converted into steel, oxygen is used to oxidise the iron.
 Steel is made by purifying iron made in the blast furnace.
 Impure iron or “pig iron” contains impurities of carbon, phosphorus, silicon and sulfur.
 It is placed in a vessel called a basic oxygen converter and oxygen is blown in to
oxidise the impurities to their oxides.
 The iron itself is not oxidised.
 Statement A is correct as CO2 is produced when carbon reacts with oxygen and heats
up the blast furnace, forming carbon dioxide:
•
C + O2 → CO2
 Statement B is correct as carbon monoxide reduces the Iron (III) oxide in the iron ore to
form iron, thereby acting as a reducing agent:
•
Fe2O3 + 3CO → 2Fe + 3CO2
 Statement C is correct as the extraction of iron does involve reduction by carbon
monoxide.
21
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14. The diagram shows a blast furnace.
In which part is iron ore changed to iron?
A
B
C
D
 Carbon monoxide reduces the iron (III) oxide in the iron ore to form iron:
•
Fe2O3 + 3CO → 2Fe + 3CO2
 This process occurs in zone 2 of the blast furnace, where the temperature is just under
1500ºC.
 The iron produced falls to the bottom of the furnace where it is tapped off as it can flow
because the temperature at the bottom is higher ( around 2000ºC) than the melting
point of iron (1538ºC).
 A is incorrect as this is where the reactants are added.
 C is incorrect as this is where the molten slag is tapped off.
 D is incorrect as this is where the molten iron is tapped off.
22
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The blast furnace
7
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15. Four reactions that take place in the blast furnace to produce iron are shown.
Which reaction is used to keep the furnace hot?
A
C + O2 → CO2
B
CO2 + C → 2CO
C
Fe2O3 + 3C → 2Fe + 3CO
D
Fe2O3 + 3CO → 2Fe + 3CO2
 This is the reaction of hot air and coke and it occurs at the bottom of the blast furnace.
 Blasts of hot air are sent in near the bottom and the carbon combusts heating up the
furnace.
 B is incorrect as this is the reduction of CO2, produced in the combustion of C, to CO.
 C and D are incorrect as these reactions are the reduction of the iron ore by carbon and
by carbon monoxide.
The blast furnace
24
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16. Iron is extracted from its ore (hematite) in the blast furnace.
Which gas is produced as a waste product?
A
carbon dioxide
B
hydrogen
C
nitrogen
D
oxygen
 In the blast furnace, iron ore is reduced to iron by reaction with carbon monoxide:
○
Fe2O3 + 3CO → 2Fe + 3CO2
 Carbon dioxide gas is the waste produced and exits the blast furnace at the top of the
tower.
 B, C and D are incorrect as these gases are not produced in the process.
Blast furnace
25
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17. Iron is extracted from hematite in a blast furnace.
Which reaction increases the temperature in the blast furnace to over 1500 °C?
A
calcium carbonate → calcium oxide + carbon dioxide
B
calcium oxide + silicon dioxide → calcium silicate
C
carbon + oxygen → carbon dioxide
D
carbon dioxide + carbon → carbon monoxide
 Air is blasted in at the bottom of the furnace where it reacts with carbon which enters
from the top.
 This reaction occurs in zone 1 on the diagram below and is used to heat the furnace to
very high temperature.
 It can do this as it is a strongly exothermic reaction which gives off a lot of heat
energy.
 A is incorrect as this is an endothermic reaction which occurs on addition of calcium
carbonate at the top of the furnace.
 B is incorrect as this is the reaction with removes silicon impurities from the furnace by
forming slag.
 D is incorrect as this is the reaction that produces the reducing agent, carbon
monoxide.
26
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Blast furnace
27
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18. Which row describes the conditions used to make steel from the iron produced by a blast
furnace?
 All three conditions are required to make steel from iron.
 Calcium oxide reacts with silicon impurities to produce calcium silicate. The
reaction is as follows:
•
CaO(s) + SiO2(s) → CaSiO3(s)
 Oxygen is added to oxidise sulfur contaminants to sulfur dioxide and carbon
impurities to carbon dioxide.
 These processes require heat.
Iron blast furnace

28
Options B, C and D do not include all of the conditions required.
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19. Molten iron from the blast furnace contains impurities.
The process of turning the impure iron into steel involves blowing oxygen into the molten iron and
adding calcium oxide.
What are the reasons for blowing in oxygen and adding calcium oxide?
blowing in oxygen
adding calcium oxide
A
carbon is removed by reacting with oxygen
reacts with acidic impurities making slag
B
carbon is removed by reacting with oxygen
reacts with slag and so removes it
C
iron reacts with the oxygen
reacts with acidic impurities making slag
D
iron reacts with the oxygen
reacts with slag and so removes it
 Steel is made by purifying iron made in the blast furnace.
 Impure iron or “pig iron” contains impurities of carbon, phosphorus, silicon and sulfur.
 It is placed in a vessel called a basic oxygen converter and oxygen is blown in to
oxidise the impurities to their oxides, hence C and D are incorrect.
 Calcium oxide is added to remove the silicon and phosphorus by reacting with their
oxides producing slag:
○
SiO2 + CaO → CaSiO3
 The slag floats on the molten iron and is removed.
 B is therefore incorrect as the calcium oxide is what produces the slag on reaction with
impurities, it does not react with the slag.
29
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Basic oxygen converter
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20. Iron from a blast furnace is treated with oxygen and with calcium oxide to make steel.
Which substances in the iron are removed?
oxygen removes
calcium oxide
removes
A
carbon
acidic oxides
B
carbon
basic oxides
C
iron
acidic oxides
D
iron
basic oxides
 The oxygen reacts with the carbon to produce carbon dioxide.
•
C(s) + O2(g) → CO2(g)
 Silicon and phosphorus are impurities found in iron.
 These react with the oxygen blown in to form non-metal oxides which are acidic.
 These are removed by reaction with calcium oxide which form slag.
 For example the reaction with silicon is:
•
31
CaO(s) + SiO(s) →CaSiO3(l)
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21. Iron is obtained from its ore in a blast furnace and is used to make steel.
Iron obtained from the blast furnace is contaminated with ......1...... .
In order to remove this substance, ......2...... is passed through the molten iron.
......3...... is also added to remove oxides of phosphorus and silicon which are ......4...... .
Which words complete the sentences about the conversion of iron to steel?
 Iron from the blast furnace contains impurities of carbon, phosphorus, silicon and
sulfur.
 Hence D can be disregarded as sand is not present.
 The impure iron is placed in a vessel called a basic oxygen converter and oxygen is
blown in to oxidise the impurities to their oxides.
 Hence A can be disregarded as nitrogen is not used.
 Calcium oxide is then added to remove the silicon and phosphorus by reacting with
their oxides producing slag:
○
SiO2 + CaO → CaSiO3
 Silicon and phosphorus are nonmetals hence their oxides are acidic.
 Therefore, C is also incorrect.
32
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22. Aluminium is manufactured by electrolysis of aluminium oxide.
The diagram shows the electrolysis cell.
anode
cathode
+
+
aluminium oxide
in molten cryolite
molten aluminium
Which statement about the process is not correct?
A
Aluminium ions gain electrons during the electrolysis and are reduced.
B
Cryolite is added to reduce the melting point of the aluminium oxide.
C
The anode and cathode are made of graphite.
D
The cathode has to be replaced regularly because it is burnt away.
the cathode is not burnt away in the process. It is the anode that is degraded over time due to
the reaction of the graphite with the oxygen gas formed there.
33
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23. Why is cryolite used during the extraction of aluminium by electrolysis?
A
It is a catalyst for the reaction.
B
It lowers the melting point of the electrolyte.
C
It protects the anodes.
D
It separates the aluminium from the electrolyte.
 Aluminium is extracted from its oxide after being treated with sodium hydroxide.
 The melting point of aluminium oxide is 2030ºC.
 By dissolving it in cryolite, the melting point is reduced to 900 - 1000ºC.
 The lower temperature is much more cost effective and safer to operate.
Extraction of aluminium
34
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24. Aluminium is extracted by electrolysis of a mixture of aluminium oxide and cryolite.
Which statement is not correct?
A
The electrodes are made from graphite.
B
The formula for aluminium oxide is Al 2O3.
C
The purpose of the cryolite is to lower the melting point of the mixture.
D
The reaction taking place at the anode is Al 3+ + 3e– → Al .

The reaction which takes place at the anode is:
•

O2- → O2 + 4 electrons.
The reaction given in D is that which occurs at the cathode.
Extraction of aluminium by electrolysis
35
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25. Iron is extracted from hematite in the blast furnace.
The hematite contains silicon(IV) oxide (sand) as an impurity.
What reacts with this impurity to remove it?
A
calcium oxide
B
carbon
C
carbon dioxide
D
slag
 Calcium oxide is used in the blast furnace as it reacts with impurities to produce calcium
silicate:
○
CaO + SiO2 → CaSiO3
 This is known as slag and is removed from the bottom of the furnace; hence D is
incorrect.
 B is incorrect as carbon is added to react with oxygen and heat up the blast furnace,
forming carbon dioxide:
○
C + O2 → CO2
 C is incorrect as the CO2 formed in the process above reacts with carbon to form carbon
monoxide, which is the reducing agent:
○
CO2 + C → 2CO
 Carbon monoxide reduces the iron (III) oxide in the iron ore to form iron:
○
36
Fe2O3 + 3CO → 2Fe + 3CO2
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26. Brass is an alloy of two metals.
Which row gives a correct use for the two metals from which brass is made?
metal 1
metal 2
A
used for electrical wiring
used for galvanising steel
B
used for galvanising steel
used for making aircraft
C
used for making aircraft
used for making cutlery
D
used for making cooking pans
used for electrical wiring
 Brass is an alloy made from 70% copper and 30% zinc.
 Copper is used in electrical wiring due to its low resistance which make it a good
conductor of electricity.
 Zinc is used in galvanising steel as it is more reactive and will thus oxidise before the
steel does (sacrificial protection).
37
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27 Zinc is extracted from zinc blende. Zinc blende is an ore of zinc and consists mainly of zinc
sulfide.
One of the steps in the process involves zinc sulfide reacting with oxygen from the air.
What is the equation for this reaction?
A
2ZnS + 3O2 → 2ZnO + 2SO2
B
2ZnS + O2 → 2Zn + SO2
C
2ZnS + O2 → 2ZnO + S
D
ZnS + 2O2 → ZnSO4
 Zinc blende is heated very strongly in the presence of oxygen producing the metal
oxide.
 The metal oxide is then reduced with carbon to produce pure zinc metal.
38
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28 Which material is not involved in the large-scale extraction of iron from iron ore?
A
bauxite
B
calcium carbonate (limestone)
C
carbon (coke)
D
hematite
 Hematite is the mineral ore of iron, which is found as iron(III) oxide, Fe2O3.
 Iron is below carbon on the reactivity series and thus can be removed from the ore by
heating with carbon in a blast furnace.
 Carbon reacts with oxygen and heats up the blast furnace, forming carbon dioxide:
○
C + O2 → CO2
 Limestone is then added which decomposes to form CO2 and CaO which removes slag:
○
CaCO3 → CO2 + CaO
 The CO2 formed in the above two equations reacts with carbon to form carbon
monoxide which is the reducing agent:
○
CO2 + C → 2CO
 Carbon monoxide reduces the Iron (III) oxide in the iron ore to form iron:
○
Fe2O3 + 3CO → 2Fe + 3CO2
 Hematite, carbon and limestone are all used in the process, hence B, C and D are
incorrect.
 Bauxite is the ore of aluminium and it is not used in the extraction of iron from hematite.
39
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29 Which process is used to extract iron from hematite in the blast furnace?
A
electrolysis
B
reduction with carbon monoxide
C
reduction with lime
D
thermal decomposition
 Hematite is the mineral ore of iron, which is found as iron(III) oxide, Fe2O3.
 Iron is below carbon on the reactivity series and thus can be removed from the ore by
heating with carbon in a blast furnace.
 Carbon reacts with oxygen and heats up the blast furnace, forming carbon dioxide:
○
C + O2 → CO2
 Limestone is then added which decomposes to form CO2 and CaO which removes slag:
○
CaCO3 → CO2 + CaO
 The CO2 formed in the above two equations reacts with carbon to form carbon
monoxide which is the reducing agent:
○
CO2 + C → 2CO
 The final step is when carbon monoxide reduces the iron (III) oxide in the iron ore to
form iron:
○
Fe2O3 + 3CO → 2Fe + 3CO2
 A is incorrect as electrolysis is not required due to the relatively low reactivity of iron.
 C is incorrect as lime is used to remove the slag produced but does not reduce the iron.
 D is incorrect as thermal decomposition is not used to extract iron.
40
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30 What is the reducing agent in the large-scale extraction of iron from iron ore?
A
air
B
carbon monoxide
C
hematite
D
limestone
 Hematite is the mineral ore of iron, which is found as iron(III) oxide, Fe2O3.
 Iron is below carbon on the reactivity series and thus can be removed from the ore by
heating with carbon in a blast furnace.
 Carbon reacts with oxygen and heats up the blast furnace, forming carbon dioxide:
○
C + O2 → CO2
 Limestone is then added which decomposes to form CO2 and CaO which removes slag:
○
CaCO3 → CO2 + CaO
 The CO2 formed in the above two equations reacts with carbon to form carbon
monoxide which is the reducing agent:
○
CO2 + C → 2CO
 The carbon monoxide reduces the Iron (III) oxide in the iron ore to form iron:
○
Fe2O3 + 3CO → 2Fe + 3CO2
 A is incorrect as air is blown in to provide oxygen but is not used to reduce the iron.
 C is incorrect as hematite is the rawore from which the iron is extracted.
 D is incorrect as even though limestone produces CO2 which later reacts with carbon to
produce carbon monoxide, it is added to produce CaO which removes slag.
41
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31 Aluminium is extracted by the electrolysis of aluminium oxide.
Which statement is not correct?
A
Aluminium ions are oxidised at the cathode.
B
Carbon dioxide is made at the anode.
C
Cryolite is added to lower the melting point of the aluminium oxide.
D
The electrodes are made from graphite.
 Aluminium is extracted from its oxide by electrolysis
 A is not correct as at the cathode the aluminium ions are reduced as they gain
electrons.
 B is correct as CO2is formed at the anode. The oxygen gas produced in the electrolysis
reaction reacts with the carbon (in the form of graphite) electrode. The graphite
electrodes have to be regularly replaced as they wear away.
 C is correct as cryolite is added to the aluminium oxide to bring its melting point from
2030ºC to 900 - 1000ºC. The lower temperature is much more costeffective and safer
to operate.
 D is correct as both electrodes are made from graphite, which is an allotrope of carbon.
42
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Extraction of aluminium
43
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32 Aluminium is extracted from bauxite by electrolysis.
Which row shows the anode material and the anode reaction?
anode material
anode reaction
A
carbon
Al 3+ + 3e– → Al
B
carbon
2O2– → O2 + 4e–
C
steel
Al 3+ + 3e– → Al
D
steel
2O2– → O2 + 4e–
 Aluminium is extracted from its oxide by electrolysis
 The anode material used in this process is graphite which is made of carbon, hence C
and D are incorrect.
 O2- ions move towards the anode (+) where they are oxidised(lose electrons) to
produce oxygen gas.
 The aluminium ions are attracted to the cathode(-) where they are reduced (gain
electrons) to form aluminium metal, hence A is also incorrect.
Extraction of aluminium
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33 Aluminium is obtained by the electrolysis of a mixture of aluminium oxide and cryolite.
Why is cryolite used?
A
as a catalyst to speed up the process
B
as a coolant to prevent the process getting too hot
C
as a solvent for aluminium oxide
D
as the main source of aluminium ions
 Aluminium is extracted from its oxide using electrolysis.
 The melting point of aluminium oxide is 2030ºC.
 By dissolving it in cryolite, the melting point is reduced to 900 - 1000ºC.
 The lower temperature is much more costeffective and safer to operate.
 The cryolite is therefore acting as a solvent, hence C is the right answer.
 A and B are incorrect as cryolite is not a catalyst nor a coolant.
 D is incorrect as the aluminium ions come from the aluminium ore, bauxite.
Extraction of aluminium
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34
Which statement about the extraction of iron in a blast furnace is not correct?
A
Calcium oxide reacts with acidic impurities.
B
Iron(III) oxide is reduced to iron by carbon dioxide.
C
Molten iron is formed at the base of the blast furnace.
D
The raw materials are hematite, limestone and coke.
 The iron is extracted by reduction with carbon monoxide, not carbon
dioxide.
 The reaction equation is:
• Fe2O3(s) + 3CO(s) → 2Fe(s) + 3CO2(g)
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35 Steel is manufactured from the iron produced in a blast furnace.
Which statement about the manufacture of iron and steel is not correct?
A
In a blast furnace, acidic impurities are removed by adding a basic oxide.
B
In a blast furnace, calcium oxide is added to remove basic impurities.
C
Oxygen is passed into the molten iron from a blast furnace to remove carbon impurities.
D
The molten iron from a blast furnace contains traces of other elements such as phosphorus.
 Calcium oxide is added to the blast furnace but not to remove basic impurities.
 CaO removes one of the main impurities in iron ore which is sand.
 The equation is:
•
CaO(s) + SiO2(s) → CaSiO3(l)
 The molten calcium silicate formed is removed as slag from the bottom of the
furnace.
47
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36 Which statement about the extraction of iron from hematite is correct?
A
Air is blown into the blast furnace to oxidise the molten iron.
B
Carbon dioxide is reduced by coke to carbon monoxide.
C
Hematite is oxidised by carbon to molten iron.
D
The slag produced is denser than molten iron.
 Carbon dioxide in the blast furnace is reduced by coke to carbon
monoxide.
 The carbon monoxide is then used to reduce the iron ore to iron.
Blast furnace reactions
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37 Zinc metal is extracted from its ore zinc blende in a similar method to that used to extract iron
from hematite.
In which way is zinc extraction different from iron extraction?
A
Carbon and carbon monoxide are the main reducing agents.
B
Hot air at the base of the furnace reacts with coke to keep the furnace hot.
C
The metal is removed as a vapour at the top of the furnace.
D
The metal oxide is added into the top of the furnace.
 Both metals are obtained by reduction with carbon from their ores in a blast furnace.
 For iron the process produces molten iron which is removed from the bottom of the
furnace.
 For zinc the metal is produced in the vapour phase and is passed out through the top
of the furnace where it is cooled and condensed.
Blast furnace for extracting zinc
49
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38 Which process is involved in the extraction of zinc from zinc blende?
A
Cryolite is added to lower the melting point of zinc blende.
B
Molten zinc blende is electrolysed.
C
Zinc blende is heated with carbon.
D
Zinc blende is roasted in air.
 During the extraction of zinc, the zinc blende is roasted in air.
 This process produces zinc oxide from zinc sulfide. The equation is:
2ZnS(s) + 3O2(g)

→ 2ZnO(s) + 2SO2(g)
The zinc oxide is then reduced to produce pure zinc.
Blast furnace for the extraction of zinc from zinc blende
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39 Which equation from the zinc extraction process shows the metal being produced by reduction?
A
ZnO + C → Zn + CO
B
2ZnS + 3O2 → 2ZnO + 2SO2
C
Zn(g) → Zn(l)
D
Zn(l) → Zn(s)
 There are three definitions for reduction:
•
when oxygen is removed from a compound.
•
when an atom, ion or molecule gains electrons in a reaction.
•
a reaction in which the oxidation number of an element is decreased.
•
ZnO + C
→ Zn + CO
 The zinc oxide loses oxygen and is reduced to produce pure zinc.
 Carbon is a good reducing agent and is often used in the extraction of metals from
their oxides.
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40 Two industrial processes that involve heating are
•
extracting iron from its ore using a blast furnace,
•
making lime.
In which of these processes is calcium carbonate used?
extracting iron
making lime
A
B
C
D
 Limestone is the compound calcium carbonate, CaCO3.
 It decomposes on heating to produce the compound CaO which is lime.
 When water is added to lime, calcium hydroxide is produced which is the
compound Ca(OH)2.
 Powdered limestone, lime and calcium hydroxide (slaked lime) all have important
industrial compounds.
 They have many uses, amongst others they are:
•
Used in the construction industry to make cement
•
Used to make glass
•
Used to neutralise acidic soils
•
Used to make steel by removing impurities from the blast furnaces
•
Used in the fabrication of paper to whiten and add bulk
 Calcium carbonate is used in blast furnaces in the extraction of iron from
hematite as it decomposes in heat of the furnace to produce lime:
• CaCO3 → CaO + CO2
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 The lime produced reacts with impurities of silicon and phosphorus by reacting
with their oxides producing slag:
• SiO2 + CaO → CaSiO3
 The slag floats on the molten iron and is removed.
 Lime is also produced from the thermal decomposition of limestone; hence A is
the right answer.
 Therefore B, C and D are incorrect.
The limestone cycle
53
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