Copper(II) sulfate solution is stored in a laboratory. A student adds excess zinc powder to the copper(II) sulfate solution and observes a colour change. Explain what happens during this reaction, including why zinc is able to displace copper from solution.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Copper(II) sulfate solution is blue. Zinc is a metal found above copper in the reactivity series.
Model answer (5 marks)
Zinc powder is added to the blue copper(II) sulfate solution.
1. Zinc displaces copper from solution – a displacement reaction.
2. Zinc is higher in the reactivity series than copper, so it is more reactive.
3. Zinc atoms lose electrons (Zn → Zn²⁺ + 2e⁻) – zinc is oxidised.
4. Copper(II) ions gain the electrons (Cu²⁺ + 2e⁻ → Cu) – copper is reduced.
5. The blue colour fades as Cu²⁺ is removed and a brown/pink solid of copper is deposited, making the solution colourless.
1. Zinc displaces copper from solution – a displacement reaction.
2. Zinc is higher in the reactivity series than copper, so it is more reactive.
3. Zinc atoms lose electrons (Zn → Zn²⁺ + 2e⁻) – zinc is oxidised.
4. Copper(II) ions gain the electrons (Cu²⁺ + 2e⁻ → Cu) – copper is reduced.
5. The blue colour fades as Cu²⁺ is removed and a brown/pink solid of copper is deposited, making the solution colourless.
Examiner tips
- Use the word ‘displacement’ and mention the reactivity series. Show the oxidation of Zn and reduction of Cu with equations. Explain the colour change in terms of Cu²⁺ removal and Cu deposition.
- common_mistakes
- :
- Saying zinc is ‘less reactive’ instead of ‘more reactive’. Forgetting to state that the blue colour fades because Cu²⁺ is removed. Not recognising the reaction as a displacement reaction.
Mark scheme (5 marks)
- Zinc displaces copper from solution / this is a displacement reaction
- Zinc is higher in the reactivity series than copper / zinc is more reactive than copper
- Zinc atoms lose electrons / zinc is oxidised
- Copper(II) ions gain electrons / copper ions are reduced
- The blue colour fades / solution becomes colourless as copper(II) ions are removed from solution AND/OR a brown/pink solid (copper) is deposited
Related
- All Edexcel A-Level Chemistry (9CH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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