Aluminium is extracted from aluminium oxide by electrolysis. The electrolyte is a molten mixture of aluminium oxide and cryolite.
Give the reason why aluminium is not extracted by heating aluminium oxide with carbon.
The melting point of aluminium oxide is 2072 ∘C2072\ ^\circ\text{C}2072 ∘C. The melting point of the mixture of aluminium oxide and cryolite is about 950 ∘C950\ ^\circ\text{C}950 ∘C. Explain why the mixture is used instead of pure aluminium oxide.
The positive electrode is made of carbon. Explain why it must be replaced regularly.
Give one reason why extracting aluminium by electrolysis is expensive.
40 exam-style questions on AQA GCSE Chemistry 4.3 Electrolysis, covering 4.3.1a The process of electrolysis, 4.3.1b Half equations in electrolysis, 4.3.2 Electrolysis of molten ionic compounds, 4.3.3 Using electrolysis to extract metals, 4.3.4 Electrolysis of aqueous solutions, and 4.3.5 Representation of reactions at electrodes as half equations. Each one has a worked solution and a mark scheme showing where the marks go.