# Crude oil is a mixture of hydrocarbons. Fractional distillation is used to separate crude oil into fractions. Explain how fractional distillation separates crude oil into fractions with different boiling points, and state one use of the fraction with the lowest boiling point.

> Edexcel A-Level Chemistry (9CH0) — Topic 3 Organic chemistry I · Explain · 5 marks

> Crude oil is a finite resource formed over millions of years from the remains of ancient organisms. It is a complex mixture of hydrocarbon molecules of different chain lengths.

## Mark scheme (5 marks)

1. Crude oil is heated and the hydrocarbons evaporate / vaporise
2. The vapours rise up the fractionating column where there is a temperature gradient (hotter at the bottom, cooler at the top)
3. Hydrocarbons condense when they reach the part of the column that is at their boiling point
4. Longer hydrocarbon chains have higher boiling points so condense lower in the column / shorter chains have lower boiling points so rise higher and condense near the top
5. The fraction with the lowest boiling point is petrol / gasoline / used as fuel for cars / used as a fuel

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](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-a209fe7a) · Published by Druglandscape Ltd.