# A chemist is given two samples of a liquid. Sample A is described as pure ethanol. Sample B is described as a mixture of ethanol and water. Explain how the chemist could use melting point data to decide which sample is the pure substance, and what result she would expect for each sample.

> Eduqas GCSE Chemistry — 1.4 The ever-changing Earth · Explain · 4 marks

## Mark scheme (4 marks)

1. The chemist measures/records the melting point (or melting point range) of each sample
2. A pure substance has a sharp (specific/precise) melting point
3. Sample A (pure ethanol) would melt at one specific/sharp temperature (accept: would match the known melting point of ethanol)
4. Sample B (the mixture) would melt over a range of temperatures (rather than at a sharp point)

## Key terms

- [pure substance](https://www.gradenine.co.uk/glossary/pure-substance)
- [melting point data](https://www.gradenine.co.uk/glossary/melting-point-data)
- [mixture](https://www.gradenine.co.uk/glossary/mixture)

## Related

- [Revision notes for Eduqas GCSE 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/a-chemist-is-given-two-samples-1be6edb3) · Published by Druglandscape Ltd.