Explain what happens in terms of oxygen and electrons during the reaction between copper(II) oxide and hydrogen. Identify which substance is oxidised and which is reduced, and state what type of overall reaction this is.

AQA A-Level Chemistry (7405) — 3.1.7 Oxidation, reduction and redox equations · Explain · 5 marks · View as Markdown

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

Copper(II) oxide reacts with hydrogen gas to form copper metal and water: CuO + H₂ → Cu + H₂O

Model answer (5 marks)

Hydrogen gas is oxidised: H₂ loses electrons and gains oxygen to form H₂O.
Copper(II) oxide is reduced: CuO loses oxygen and gains electrons to give Cu metal.
Thus CuO (Cu²⁺) is the oxidising agent and H₂ is the reducing agent.
The overall process is a redox reaction, with simultaneous oxidation of H₂ and reduction of CuO.

Examiner tips

  • Use the term ‘oxidised’ for H₂ and ‘reduced’ for CuO; mention electron transfer. Identify the reducing agent (H₂) and oxidising agent (CuO). State the reaction type as a redox reaction.
  • common_mistakes
  • :
  • Saying ‘hydrogen is reduced’ instead of oxidised. Forgetting to mention that CuO loses oxygen. Calling the reaction a combustion or substitution instead of redox.

Mark scheme (5 marks)

  1. Hydrogen gains oxygen (to form water), so hydrogen is oxidised
  2. Copper(II) oxide loses oxygen (to form copper), so copper(II) oxide / CuO is reduced
  3. Copper(II) oxide / Cu²⁺ gains electrons (is reduced) OR hydrogen loses electrons (is oxidised) — in terms of electron transfer
  4. Hydrogen / H₂ is the reducing agent
  5. The overall reaction is a redox reaction (because oxidation and reduction occur simultaneously)

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