Zinc can be extracted from zinc oxide by reduction with carbon. Describe what happens during this process and explain why this method is suitable for zinc but cannot be used to extract magnesium from magnesium oxide.

Edexcel GCSE Chemistry (1CH0) — 4.1 Obtaining and using metals · Describe and Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Zinc oxide is heated with a carbon source (e.g. charcoal). The carbon reacts with the oxygen in ZnO to form CO/CO₂, leaving elemental zinc:
ZnO + C → Zn + CO/CO₂
The zinc produced is a liquid at the reaction temperature and can be collected.
This works because zinc is less reactive than carbon; carbon can displace zinc from its oxide.
Magnesium, however, is more reactive than carbon. Carbon cannot remove the oxygen from MgO, so the reduction does not occur. Magnesium must therefore be extracted by electrolysis of molten MgO.

Examiner tips

  • Show the chemical equation for the reduction of ZnO by carbon.
  • Explain the relative reactivity of Zn and Mg with carbon.
  • Mention that Mg is more reactive than C, preventing reduction.
  • Use the term ‘electrolysis’ for Mg extraction.

Common mistakes

  • Writing the reaction as ZnO + C → ZnO + C instead of Zn + CO/CO₂.
  • Claiming that carbon can reduce MgO without noting the reactivity difference.
  • Forgetting to state that zinc is liquid and can be collected.

Mark scheme (4 marks)

  1. Zinc oxide is heated with carbon
  2. Carbon reduces the zinc oxide, removing oxygen from it to produce zinc (metal)
  3. Zinc is less reactive than carbon (so carbon can displace it / so reduction with carbon is possible)
  4. Magnesium is more reactive than carbon so carbon cannot reduce magnesium oxide / electrolysis must be used instead

Key terms in this question

reduction · reduction with carbon

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