Zinc can be extracted from zinc oxide by heating it with carbon. However, sodium cannot be extracted from sodium oxide in the same way. Using your knowledge of the reactivity series, explain why carbon can be used to extract zinc but not sodium.

WJEC GCSE Chemistry (Wales) — 2.3 Metals and their extraction · Explain · 4 marks · View as Markdown

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

Zinc oxide is an ore of zinc. Sodium is a very reactive metal found in group 1 of the periodic table.

Model answer (4 marks)

Carbon can only displace metals that are less reactive than itself. Zinc is less reactive than carbon, so carbon reduces zinc oxide to zinc:
ZnO + C → Zn + CO₂.
Sodium is more reactive than carbon; therefore carbon cannot reduce sodium oxide. Sodium must be extracted by a different method, e.g. electrolysis of molten Na₂O or NaCl.

Examiner tips

  • State the reactivity comparison first, then give the reaction for zinc, and explain why it fails for sodium.
  • Use the exact phrase ‘less reactive than carbon’ and ‘more reactive than carbon’ to match the mark scheme.

Common mistakes

  • Confusing the direction of displacement (writing carbon displacing zinc instead of reducing it).
  • Forgetting to mention that sodium requires electrolysis rather than a carbon reduction.

Mark scheme (4 marks)

  1. Carbon can only displace / reduce metals that are less reactive than carbon itself
  2. Zinc is less reactive than carbon, so carbon can displace / reduce zinc from zinc oxide
  3. Sodium is more reactive than carbon, so carbon cannot displace / reduce sodium from its oxide
  4. Sodium must be extracted by a different method such as electrolysis

Key terms in this question

reactivity series

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