# Ethanol is widely used as a solvent and can also be used as a fuel. Describe the complete combustion of ethanol and explain why ethanol produced by fermentation can be considered carbon neutral, whilst ethanol produced by hydration of ethene cannot.

> AQA A-Level Chemistry (7405) — 3.3.5 Alcohols · Describe and Explain · 5 marks

## Mark scheme (5 marks)

1. Complete combustion of ethanol produces carbon dioxide and water (only)
2. The carbon and hydrogen in ethanol are oxidised during combustion
3. Fermentation uses plants/sugar/glucose as a feedstock, which absorb carbon dioxide from the atmosphere as they grow (via photosynthesis)
4. So the CO₂ released when ethanol (from fermentation) burns is balanced/offset by the CO₂ absorbed during plant growth, giving an overall neutral carbon balance
5. Ethanol from hydration of ethene uses ethene from cracking crude oil, which is a finite/non-renewable fossil fuel source, so the CO₂ released on combustion is not offset by any uptake

## Key terms

- [complete combustion](https://www.gradenine.co.uk/glossary/complete-combustion)
- [fermentation](https://www.gradenine.co.uk/glossary/fermentation)
- [carbon neutral](https://www.gradenine.co.uk/glossary/carbon-neutral)
- [hydration](https://www.gradenine.co.uk/glossary/hydration)

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/ethanol-is-widely-used-as-a-c7940453) · Published by Druglandscape Ltd.