When copper(II) oxide reacts with hydrogen gas, copper and water are formed. Which substance is oxidised and which is reduced in this reaction? Give a reason for each.
Generated by claude-sonnet-4-6 · 2026-06-26 00:54 · grounding rag
Model Answer
The reaction is: $\text{CuO} + \text{H}_2 \xrightarrow{\text{Heat}} \text{Cu} + \text{H}_2\text{O}$
Hydrogen is oxidised — because it gains oxygen (to form water).
Copper(II) oxide is reduced — because it loses oxygen (to form copper).
This is a redox reaction, where oxidation and reduction occur simultaneously.
Source: Chapter 1, Section 1.2.5 — Oxidation and Reduction
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Explanation
- Examiners award 1 mark for the equation, 1 mark for identifying the oxidised substance with reason, and 1 mark for identifying the reduced substance with reason.
- The key definitions to apply: gain of oxygen = oxidised; loss of oxygen = reduced.
- Always write the balanced equation first — it shows you clearly which substance gains and which loses oxygen.
- Do not confuse: CuO is reduced (it gives away oxygen), H₂ is oxidised (it receives oxygen). A common mistake is to reverse these.