Copper(II) oxide is a black solid. When copper(II) oxide is heated with carbon, a displacement reaction occurs, producing copper metal and carbon dioxide. Explain what has happened to the copper and the carbon in this reaction in terms of oxidation and reduction, and identify which substance is the oxidising agent.

OCR A-Level Chemistry B: Salters (H433) — 2.3 Acid-base and redox reactions · Explain · 5 marks · View as Markdown

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

Copper(II) oxide is a black solid that reacts with carbon when heated. The products of the reaction are copper metal and carbon dioxide gas.

Model answer (5 marks)

Copper ions in CuO are reduced to Cu metal – they gain electrons (or lose oxygen). Carbon is oxidised to CO₂ – it loses electrons (or gains oxygen). CuO is the oxidising agent.

Examiner tips

  • Use the terms ‘reduced’ and ‘oxidised’ with the correct species; mention electron transfer or oxygen loss/gain; state CuO as oxidising agent.
  • Show the change in oxidation state: Cu²⁺→Cu⁰, C→C⁴⁺.
  • Keep answer brief – 5 marks only.
  • Use UK spelling (oxidised).

Common mistakes

  • Saying carbon is reduced instead of oxidised.
  • Calling copper metal the oxidising agent.
  • Using ‘gain oxygen’ for copper instead of ‘lose oxygen’.”

Mark scheme (5 marks)

  1. Copper(II) oxide / copper ions have been reduced
  2. Copper (ions) have gained electrons OR oxygen has been removed from copper(II) oxide
  3. Carbon has been oxidised
  4. Carbon has gained oxygen OR carbon has lost electrons
  5. Copper(II) oxide is the oxidising agent

Key terms in this question

oxidation · reduction · oxidising agent

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