# When copper(II) oxide reacts with hydrogen gas, copper metal and water are produced. The equation for this reaction is: CuO + H₂ → Cu + H₂O. Explain what has happened to the copper and to the hydrogen in terms of oxidation and reduction, using both the oxygen-based and electron-based definitions.

> Edexcel A-Level Chemistry (9CH0) — 3.1 Oxidation and reduction · Explain · 5 marks

> Copper(II) oxide is a black solid. When hydrogen gas is passed over heated copper(II) oxide, a pink-brown solid forms and water vapour is produced.

## Mark scheme (5 marks)

1. Copper(II) oxide / copper ions have been reduced
2. Reduction defined in terms of oxygen: copper(II) oxide loses oxygen
3. Hydrogen has been oxidised
4. Oxidation defined in terms of oxygen: hydrogen gains oxygen (to form water)
5. This is a redox reaction because oxidation and reduction happen simultaneously / at the same time

## Key terms

- [oxidation](https://www.gradenine.co.uk/glossary/oxidation)
- [reduction](https://www.gradenine.co.uk/glossary/reduction)

## 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)
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