Section 5a: extraction and uses of metals Extraction of metals 5.1

Section 5a: extraction and uses of metals
Extraction of metals
5.1 explain how the methods of extraction of the metals in this section are related to their positions
in the reactivity series
The ease of obtaining a pure metal from its ore depends on the reactivity of the metal. Ore = a mixture
of rock which contains a compound with the metal in it.
The less reactive metals are easily removed from their ores as it only takes heating to do this. Reactive
metals are difficult to obtain as their oxides or salts are difficult to decompose so a lot of energy is
needed which is why they can only be reduced by using electrolysis. The unreactive metals do not
need extraction as they are found pure in nature although copper is electrolysed further as it needs to
be very pure to be used as a conductor of electricity.
reactivity series
method of extraction
reduction using electrolysis
reduction by heating with carbon
decomposition by heating alone (followed by electrolysis)
found pure
Extraction of aluminium
5.2 describe and explain the extraction of aluminium from purified aluminium oxide by
electrolysis, including
i the use of molten cryolite as a solvent and to decrease the required operating temperature
ii the need to replace the positive electrodes
iii the cost of the electricity as a major factor
5.3 write ionic half-equations for the reactions at the electrodes in aluminium extraction.
Ore = bauxite; bauxite is a type of rock which has mainly aluminium oxide but also has some
impurities like iron oxide and silica;
starting chemical: aluminium oxide
 electrolytic cell with carbon electrodes; negative electrode in sides of the cell.
 aluminium oxide is molten by electrical heating; the large current which is used to electrolyse
the aluminium oxide releases heat energy to keep the aluminium oxide molten.
to help this process, cryolite is added to lower the operating temperature and the melting point of
the mixture. The molten cryolite also acts as a solvent.
very large amounts of current which is why most aluminium smelters are near power stations and
why this is an expensive process;
 after some time the positive carbon electrodes need to be replaced as they react with oxygen
producing carbon dioxide.
Electrolytic cell used to electrolyse aluminium oxide:
Section 5 a extraction of metals
Label all the parts and add the equations of all the reactions occurring in the electrolytic cell
Oxygen and carbon dioxide (formed when the oxygen
reacts with the carbon rods; a reaction made easy by
the large amount of heat energy; carbon electrodes get
eroded away and need to be replaced every so often)
2O2- (l)  O2 (g) + 4e-
Molten aluminium
+ 3e-  Al (s)
4Al3+(l) + 12e-  4Al (s)
6O2- (l)  3O2 (g) + 12e-
overall equation :
4Al3+(l) + 6O2- (l)  4Al (s) + 3O2 (g)
2Al2O3 
4Al (s) + 3O2 (g)
Extraction of iron
5.4 describe and explain the main reactions involved in the extraction of iron from iron ore
(haematite), using coke, limestone and air in a blast furnace
Iron extraction is carried out in a blast furnace using the following raw materials:
raw material
hot air
what it is used for?
As fuel and to provide the carbon to make the reducing agent carbon monoxide
Contains the iron oxide
To remove impurities
Provides the heat and oxygen to make the reducing agent
On the diagram of the blast furnace below label all chemical.
Section 5 a extraction of metals
The table summarises the five reactions which go on in the blast furnace.
Carbon burning to make carbon dioxide (this
provides the heat)
C (s) + O2 (g) 
Carbon dioxide reacting with carbon (at the top
of the furnace there is little oxygen) to form
carbon monoxide
C (s) + CO2 (g) 
Carbon monoxide reduces the iron oxide
(this is the main reaction)
Fe2O3 (g) + 3CO (g)
Calcium carbonate decomposing
CaCO3 (s)  CaO(s) + CO2 (g) (waste gas)
Calcium oxide reacting with silicon dioxide to
form slag
CaO (s) + SiO2 (s) 
CO2 (g)
2CO (g)
2Fe (s) + 3CO2 (g)
CaSiO3 (s)
Uses of iron
5.5 explain the uses of aluminium and iron, in terms of their properties
The pig iron obtained from the blast furnace is still impure as there is about 5% carbon, silicon,
phosphorus and sulfur in it which makes it rather hard and brittle and not very useful.
Section 5 a extraction of metals
Its properties are modified by first lowering the amount of carbon, silicon, phosphorus and sulfur in it
and then alloying it with other elements. When that happens the product is called steel.
There are hundreds of alloys of steel, each one with its own properties (some only differ in the carbon
Conversion to steel (=alloy); the properties of iron are changed by the controlled addition of other
elements like carbon, nickel, chromium, tungsten, etc.
Type of steel
Typical composition
Mild steel
99.5% iron, 0.5 %
Easily worked, strong as it has
lost most brittleness
Hard steel
99 % iron, 1 % carbon
Tough and brittle
Stainless steel
74% iron, 18%
chromium, 8% nickel
Tough, does not corrode
Tungsten steel
95% iron, 5 %
Tough, hard, even at high
Car bodies and
Chemical plant and
Uses of aluminium
Aluminium is used for the following:
in the manufacture of aircraft, car bodies, step ladders, … because of its strength and low density;
in food containers because of its resistance to corrosion (because of its protective aluminium oxide
layer); also aluminium window frames rely on this property.
in overhead cables because of its low density and good electrical conductivity.
Section 5 a extraction of metals