Explain why aluminium cannot be extracted from its ore by reduction with carbon, and state the method used instead to extract aluminium.

AQA GCSE Chemistry (8462) — 4.4.3 Electrolysis · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Aluminium is more reactive than carbon, so carbon cannot displace aluminium from its oxide.
The reduction of aluminium oxide therefore requires a method that can overcome the high reduction potential of Al³⁺.
Electrolysis is used: the ore (aluminium oxide) is melted (or dissolved) so that Al³⁺ and O²⁻ ions are free to move.
The molten oxide is electrolysed to give aluminium metal at the cathode and oxygen gas at the anode.

Examiner tips

  • Use the phrase ‘more reactive than carbon’ to show understanding of reactivity series. Explain that carbon cannot reduce Al³⁺ because it is less reactive. State that electrolysis is required and that the ore must be molten for ion mobility. Keep the answer concise to fit the 4‑mark limit.

Common mistakes

  • Writing that aluminium can be extracted by carbon reduction. Forgetting to mention that the ore must be molten for electrolysis. Using vague terms like ‘chemical reaction’ instead of ‘electrolysis’.

Mark scheme (4 marks)

  1. Aluminium is more reactive than carbon
  2. Therefore carbon cannot displace/reduce aluminium (from its oxide)
  3. Electrolysis is used to extract aluminium
  4. The aluminium ore/compound must be molten (or dissolved) so that the ions are free to move

Key terms in this question

reduction with carbon

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