# Describe how fractional distillation separates crude oil into fractions, and explain why fractions collected near the top of the fractionating column have lower boiling points than those collected near the bottom.

> AQA A-Level Chemistry (7405) — 3.3.10 Aromatic chemistry (A-Level only) · Describe and Explain · 5 marks

## Mark scheme (5 marks)

1. Crude oil is heated so that it evaporates / vaporises
2. The vapour rises up the fractionating column
3. Different fractions condense at different levels / temperatures in the column and are tapped off
4. Fractions near the top contain molecules with shorter / fewer carbon atom chains
5. Shorter hydrocarbon molecules have lower boiling points (so they condense higher up the column where it is cooler)

## Key terms

- [fractional distillation](https://www.gradenine.co.uk/glossary/fractional-distillation)
- [fractions](https://www.gradenine.co.uk/glossary/fractions)
- [fractionating column](https://www.gradenine.co.uk/glossary/fractionating-column)
- [boiling point](https://www.gradenine.co.uk/glossary/boiling-point)

## 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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/describe-how-fractional-distillation-separates-crude-e7600d3d) · Published by Druglandscape Ltd.