# Crude oil is separated by fractional distillation. Explain how the fractionating column separates crude oil into fractions, and describe two properties of shorter-chain hydrocarbons compared with longer-chain hydrocarbons.

> AQA A-Level Chemistry (7405) — 3.3.11 Amines (A-Level only) · Explain · 5 marks

## Mark scheme (5 marks)

1. Crude oil is heated and the hydrocarbons evaporate / vaporise
2. Hydrocarbons condense at different temperatures / levels in the column because they have different boiling points
3. Each fraction contains molecules with a similar number of carbon atoms
4. Shorter-chain hydrocarbons have a lower boiling point (than longer-chain hydrocarbons)
5. Shorter-chain hydrocarbons are more flammable OR less viscous (more runny) than longer-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)
- [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/crude-oil-is-separated-by-fractional-aa8c2b67) · Published by Druglandscape Ltd.