# A pharmacist is checking the purity of a white powder that is supposed to be a single painkiller compound. She heats a small sample carefully and records the temperature at which it melts. Explain how the melting point data can be used to decide whether the powder is a pure substance or a mixture.

> Eduqas GCSE Chemistry — 1.1 The nature of substances and chemical reactions · Explain · 4 marks

> The powder is reported to melt at exactly 153 °C. A reference book states that the pure painkiller compound has a melting point of 153 °C.

## Mark scheme (4 marks)

1. A pure substance melts at a single, sharp (specific) temperature
2. A mixture melts over a range of temperatures (not at one fixed point)
3. The powder melts sharply at 153 °C, which matches the reference value for the pure compound
4. This indicates the powder is a pure substance (not a mixture)

## Key terms

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

## 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-pharmacist-is-checking-the-purity-bce1ee28) · Published by Druglandscape Ltd.