Section 5a worksheet extraction metals answers

Section 5 a
Extraction of metals
(adapted from
Extraction of iron in the blast furnace
(a) List and describe the four principal raw materials (including air) which are used in the blast furnace.
Carefully explain the function of each raw material used.
raw material
what it is used for?
As fuel and to provide the carbon to make the reducing agent carbon
Contains the iron oxide
To remove impurities
Provides the heat and oxygen to make the reducing agent
hot air
(b) Draw a diagram to show the outline of the structure of a blast furnace and mark on it the following
labels: hot air, raw materials (ore, coke, limestone), hot waste gases , reaction zone, melting zone, slag,
molten iron tapped off.
See textbook page 278
(c) Describe, with the help of word/symbol equations, the five chemical reactions for the various stages
of the process.
Carbon burning to make carbon dioxide (this
provides the heat) (stage 1)
Carbon dioxide reacting with carbon (at the top of the
furnace there is little oxygen) to form carbon
monoxide (stage 2)
Carbon monoxide reduces the iron oxide
(this is the main reaction) (stage 3!!!)
C (s) + O2 (g) 
Calcium carbonate decomposing
CaCO3 (s)  CaO(s) + CO2 (g) (waste gas)
Calcium oxide reacting with silicon dioxide to form
CaO (s) + SiO2 (s) 
CO2 (g)
C (s) + CO2 (g) 
2CO (g)
Fe2O3 (g) + 3CO (g)
2Fe (s) + 3CO2 (g)
CaSiO3 (s)
(d) the limestone reaction to remove silica impurities occurs in two stages (some texts combine these
equations to give CaCO3 + SiO2 ==> CaSiO3 + CO2
(1) CaCO3 ==> CaO + CO2
(2) CaO + SiO2 ==> CaSiO3
What type of reaction is (1)? Thermal decomposition
(2) If calcium oxide is a basic oxide, what sort of oxide is silicon dioxide? acidic
Why do they react together and what sort of compound is calcium silicate? Neutralization and salt
(e) Carefully explain why reaction for stage 3: iron(III) oxide + carbon monoxide ==> …. is an example of
a REDOX reaction i.e. it involves an oxidation and a reduction. Carbon monoxide is oxidized as it reduces
the iron oxide.
(f) (i) State what is oxidised in the reaction for stage 1. Carbon is oxidized.
(ii) State what is oxidised, and to what, and what is reduced, and to what, in the reaction for stage 2
Carbon is oxidized to carbon monoxide whilst carbon dioxide is reduced to carbon monoxide.
(g) Describe several uses of iron including steel. Car bodies, construction, cutlery, machine parts, ..
Extraction of aluminium
(a) What is the main ore of aluminium called? What is the name and formula of the principal aluminium
compound in it? Bauxite, aluminium oxide, Al2O3
(b) Aluminium is extracted from its ore by electrolysis. What does this mean? Aluminium oxide is broken
down into aluminium and oxygen using electricity.
(c) Sketch in outline the electrolysis cell, add labels to show: bauxite input, carbon anodes (+),
electricity supply, aluminium output, carbon cathode (-), waste gases
See text book p 117
(d) Questions on the electrolysis process:
(1) Why is cryolite added to the bauxite ore in the electrolysis cell? To lower the temperature at
which the mixture melts/lower operating temperature.
(2) Why is it expensive to produce aluminium by this method? Needs large amounts of current to
both heat the mixture and provide electrons for the reaction.
(3) Give the names and symbols of the two ions free to move in the molten ore. Where and why do
theses ions move to? Al3+ to the cathode and O2- to the anode as they are attracted to the
oppositely charged electrode.
(4) Give the two electrode equations to show the formation of aluminium at the cathode(-) and
oxygen at the anode(+). Explain the changes in terms of oxidation and reduction
cathode: reduction: Al3+(l) + 3e-  Al (s)
anode: oxidation: 2O2- (l)  O2 (g) + 4e-
(5) Why do the carbon anodes have to be replaced regularly? Is there any danger of a toxic gas
being produced? Carbon form the anode reacts with oxygen to form carbon dioxide; there is the
possibility of formation of carbon monoxide which is toxic.
(6) Is the electrolysis of molten aluminium oxide an exothermic or endothermic chemical change
and explain your answer. Endothermic process as it needs energy to keep the reaction going.
(e) The uses of aluminium
(1) Describe some everyday uses of aluminium. Airplanes, car bodies, step ladders, food cans,
window frames,
(2) Give two good reasons for recycling aluminium cans. Reduce mining of bauxite and lower
carbon dioxide emissions as less electricity is needed.
(3) Give three good reasons for using aluminium alloys for aircraft wings. Low density, strong and
does not corrode
(4) Aluminium is used for window frames but theoretically it is reactive enough to corrode away fairly
rapidly. Explain why this does not happen. Aluminium forms an oxide layer on the outside which
protects it against corrosion of reagents such as water.