When copper(II) oxide reacts with hydrogen gas, copper metal and water are produced. The equation for this reaction is: CuO + H₂ → Cu + H₂O. Explain what has happened to the copper and to the hydrogen in terms of oxidation and reduction, using both the oxygen-based and electron-based definitions.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Copper(II) oxide is a black solid. When hydrogen gas is passed over heated copper(II) oxide, a pink-brown solid forms and water vapour is produced.
Model answer (5 marks)
Copper(II) oxide is reduced to copper metal. In the oxygen‑based definition, CuO loses one oxygen atom, so the copper ion is reduced.
Hydrogen is oxidised to water. In the oxygen‑based definition, H₂ gains one oxygen atom to form H₂O, so hydrogen is oxidised.
This is a redox reaction because oxidation and reduction occur simultaneously.
Hydrogen is oxidised to water. In the oxygen‑based definition, H₂ gains one oxygen atom to form H₂O, so hydrogen is oxidised.
This is a redox reaction because oxidation and reduction occur simultaneously.
Examiner tips
- Use the word ‘reduced’ for copper and ‘oxidised’ for hydrogen; include the oxygen‑based explanation for each.
- Show that CuO loses O and H₂ gains O to emphasise simultaneous change.
- Mention that the reaction is redox because both processes happen at the same time.
Common mistakes
- Saying ‘copper is oxidised’ or ‘hydrogen is reduced’ – the opposite of what actually occurs.
- Omitting the oxygen‑based explanation or the simultaneous nature of the redox process.
Mark scheme (5 marks)
- Copper(II) oxide / copper ions have been reduced
- Reduction defined in terms of oxygen: copper(II) oxide loses oxygen
- Hydrogen has been oxidised
- Oxidation defined in terms of oxygen: hydrogen gains oxygen (to form water)
- This is a redox reaction because oxidation and reduction happen simultaneously / at the same time
Key terms in this question
Related
- All Edexcel A-Level Chemistry (9CH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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