# Explain why zinc displaces copper from a solution of copper(II) sulfate, with reference to the standard electrode potentials of the two half-reactions involved.

> IB DP Chemistry Standard Level (2023 syllabus) — R3.2 Electron transfer reactions · Explain · 4 marks

> The standard electrode potentials for the relevant half-reactions are: Cu²⁺(aq) + 2e⁻ → Cu(s), E° = +0.34 V and Zn²⁺(aq) + 2e⁻ → Zn(s), E° = −0.76 V.

## Mark scheme (4 marks)

1. Zinc is oxidised (loses electrons) and copper(II) ions are reduced (gain electrons), identifying the correct direction of electron transfer.
2. The standard electrode potential of zinc (−0.76 V) is more negative than that of copper (+0.34 V), so zinc is the stronger / better reducing agent.
3. The overall cell potential (E°cell) is positive, calculated as E°(cathode) − E°(anode) = +0.34 − (−0.76) = +1.10 V, indicating a spontaneous reaction.
4. Because E°cell is positive, the reaction is thermodynamically feasible / spontaneous, so zinc does displace copper from solution.

## Key terms

- [standard electrode potential](https://www.gradenine.co.uk/glossary/standard-electrode-potential)

## Related

- [Revision notes for IB DP Chemistry Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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