# A student constructs an electrochemical cell using a standard manganese(II)/manganese half-cell and a standard tin(II)/tin half-cell connected by a salt bridge. The standard electrode potentials are: Mn²⁺(aq) + 2e⁻ ⇌ Mn(s), E° = −1.18 V and Sn²⁺(aq) + 2e⁻ ⇌ Sn(s), E° = −0.14 V. Explain how the standard electrode potentials are used to predict the overall cell potential, identify which half-cell acts as the negative electrode, and describe the role of the salt bridge in this cell.

> Edexcel A-Level Chemistry (9CH0) — 14.1 Electrode potentials and electrochemical cells · Explain · 5 marks

> Standard electrode potentials: Mn²⁺(aq)/Mn(s), E° = −1.18 V; Sn²⁺(aq)/Sn(s), E° = −0.14 V.

## Mark scheme (5 marks)

1. The overall cell potential (e.m.f.) is calculated by subtracting the less positive (more negative) electrode potential from the more positive electrode potential, giving E°cell = −0.14 − (−1.18) = +1.04 V
2. The manganese half-cell acts as the negative electrode because it has the more negative standard electrode potential (−1.18 V)
3. Oxidation occurs at the manganese electrode (negative electrode); manganese is oxidised to Mn²⁺ ions
4. The salt bridge completes the electrical circuit by allowing ions to flow between the two half-cells
5. The salt bridge maintains electrical neutrality in each half-cell by balancing the build-up of charge as ions are produced or consumed

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-constructs-an-electrochemical-cell-737de5e0) · Published by Druglandscape Ltd.