# Crude oil is a mixture of hydrocarbons. Explain how fractional distillation separates crude oil into fractions, and state one use of the fraction with the shortest hydrocarbon chains.

> Eduqas A-Level Chemistry — 2.5 Hydrocarbons · Explain · 5 marks

> Crude oil is an important raw material obtained from beneath the Earth's surface. It contains hydrocarbons of different chain lengths, which can be separated and used as fuels and feedstocks.

## Mark scheme (5 marks)

1. Crude oil is heated / vaporised so that the hydrocarbons evaporate
2. Hydrocarbons have different boiling points (due to different chain lengths)
3. The vapours rise up the fractionating column where there is a temperature gradient (cooler at the top)
4. Hydrocarbons condense and are collected at different levels / fractions where the temperature matches their boiling point
5. A correct use of the fraction with the shortest chains — e.g. refinery gas used as a fuel / LPG for cooking or heating

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Chemistry](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-a-mixture-of-cad638eb) · Published by Druglandscape Ltd.