# A student wants to separate a mixture of two liquids, ethanol and water, to obtain a sample of pure ethanol. Explain why simple distillation would not be suitable for this purpose and describe how fractional distillation could be used instead to obtain pure ethanol.

> WJEC A-Level Chemistry (Wales) — 1.4 States of matter · Explain and Describe · 5 marks

> Ethanol boils at 78 °C and water boils at 100 °C. Both liquids are miscible, meaning they mix completely together.

## Mark scheme (5 marks)

1. Simple distillation is not suitable because the boiling points of ethanol and water are too close together (only 22 °C apart) / the liquids cannot be separated completely by simple distillation because both vapourise at similar temperatures.
2. In fractional distillation, the mixture is heated in a fractionating column.
3. The vapour rises up the fractionating column and the liquid with the lowest boiling point (ethanol) reaches the top first / condenses lower in the column for the less volatile liquid.
4. The ethanol vapour is cooled / condensed in a condenser and collected as a liquid.
5. The two liquids can be separated into different fractions because they have different boiling points.

## Key terms

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

## Related

- [Revision notes for WJEC A-Level Chemistry (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain and Describe" 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/a-student-wants-to-separate-a-eda7c991) · Published by Druglandscape Ltd.