Copper can be displaced from copper sulfate solution by adding zinc metal. In this reaction, zinc atoms lose electrons and copper ions gain electrons. Explain what is meant by oxidation and reduction in terms of electron transfer, and use this to identify which substance is oxidised and which is reduced in this reaction.

Eduqas A-Level Chemistry — 1.8 Redox · Explain · 5 marks · View as Markdown

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

When zinc metal is added to blue copper sulfate solution, the blue colour fades and a reddish-brown solid forms. The ionic equation for this reaction is: Zn + Cu²⁺ → Zn²⁺ + Cu

Model answer (5 marks)

Oxidation is the loss of electrons. Reduction is the gain of electrons.
In the reaction Zn + Cu²⁺ → Zn²⁺ + Cu, zinc atoms lose electrons to form Zn²⁺, so zinc is oxidised.
Copper ions gain the electrons lost by zinc and are reduced to copper metal.

Examiner tips

  • Use the terms ‘oxidation’ and ‘reduction’ explicitly; examiners look for the electron‑transfer definition.
  • State which element loses electrons and which gains them, linking to the products.
  • Keep the answer concise – 5 marks can be earned with a short, clear explanation.

Common mistakes

  • Confusing ‘oxidised’ with ‘reduced’ or vice versa.
  • Omitting the electron‑transfer definition of oxidation/reduction.
  • Writing a long narrative instead of a brief, point‑wise answer.

Mark scheme (5 marks)

  1. Oxidation is the loss of electrons
  2. Reduction is the gain of electrons
  3. Zinc is oxidised
  4. Because zinc atoms lose electrons (to form Zn²⁺)
  5. Copper ions (Cu²⁺) are reduced because they gain electrons (to form Cu atoms)

Key terms in this question

oxidation · reduction · electron transfer

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