# Crude oil is separated by fractional distillation. Explain how fractional distillation separates crude oil into fractions, and state two ways in which a short-chain hydrocarbon fraction differs in its properties from a long-chain hydrocarbon fraction.

> AQA A-Level Chemistry (7405) — 3.3.16 Chromatography (A-Level only) · Explain · 5 marks

## Mark scheme (5 marks)

1. Crude oil is heated / vaporised so that hydrocarbons evaporate
2. Hydrocarbons condense / are collected at different levels / temperatures because they have different boiling points
3. Fractions contain molecules with a similar number of carbon atoms
4. Short-chain hydrocarbons have a lower boiling point (than long-chain hydrocarbons)
5. Short-chain hydrocarbons are more flammable OR less viscous / more runny (than long-chain hydrocarbons)

## Key terms

- [fractional distillation](https://www.gradenine.co.uk/glossary/fractional-distillation)
- [fraction](https://www.gradenine.co.uk/glossary/fraction)
- [hydrocarbon](https://www.gradenine.co.uk/glossary/hydrocarbon)

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/crude-oil-is-separated-by-fractional-f5ad6adc) · Published by Druglandscape Ltd.