# Explain how an electrochemical cell produces a voltage, including the role of the two half-cells and the salt bridge.

> AQA A-Level Chemistry (7405) — 3.1.11 Electrode potentials and electrochemical cells (A-Level only) · Explain · 5 marks

> An electrochemical cell can be made by connecting two different metal/metal ion half-cells. For example, a zinc half-cell (zinc rod in zinc sulfate solution) can be connected to a copper half-cell (copper rod in copper sulfate solution).

## Mark scheme (5 marks)

1. Each half-cell involves a different oxidation or reduction reaction (half-reaction) occurring at the electrode
2. Electrons are transferred through the external circuit from the more reactive metal (negative electrode) to the less reactive metal (positive electrode)
3. The difference in reactivity (or tendency to lose electrons / electrode potential) between the two metals causes the voltage / potential difference
4. The salt bridge completes the electrical circuit by allowing ions to move between the two solutions
5. The salt bridge maintains electrical neutrality in each half-cell by balancing the build-up of charge

## Key terms

- [electrochemical cell](https://www.gradenine.co.uk/glossary/electrochemical-cell)
- [half-cell](https://www.gradenine.co.uk/glossary/half-cell)
- [salt bridge](https://www.gradenine.co.uk/glossary/salt-bridge)

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-an-electrochemical-cell-produces-7afa9dc1) · Published by Druglandscape Ltd.