Metals above carbon in the reactivity series
4 marks · NormalAluminium is extracted from aluminium oxide using electrolysis.
Name the substance in which aluminium oxide is dissolved for the electrolysis process.
Write the ionic equation for the reaction at the cathode during the electrolysis of aluminium oxide.
Write the ionic equation for the reaction at the anode during this process.
Explain why the extraction of aluminium by electrolysis is much more expensive than extracting iron by reduction with carbon.
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(a) Cryolite
(b)
(c)
(d) Because electrolysis requires large amounts of electricity, making it much more expensive than using carbon for iron extraction.
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Marking points
B1 (a) · 1 mark · States cryolite as the solvent/dissolving agent.
B2 (b) · 1 mark · Gives correct cathode half-equation: .
B3 (c) · 1 mark · Gives correct anode half-equation: .
B4 (d) · 1 mark · Mentions (huge) electricity cost as main reason for higher expense.
Worked solution
a) Aluminium oxide is dissolved in molten cryolite to lower its melting point.
b) At the cathode:
c) At the anode:
d) Electrolysis uses a large amount of electricity, so it is much more expensive than reduction of iron oxide with carbon.