# A pharmacist is checking the purity of a white powder that should be a single painkiller compound. She measures the melting point of a pure sample of the compound and finds it melts sharply at 153 °C. She then measures the melting point of the powder she has been supplied with and finds it melts over the range 141 °C to 149 °C. Explain what the melting point data tells the pharmacist about the powder she has been supplied with.

> Eduqas GCSE Chemistry — 1.2 Atomic structure and the periodic table · Explain · 4 marks

## Mark scheme (4 marks)

1. The supplied powder is not a pure substance / is impure
2. A pure substance has a sharp / specific melting point, but the powder melts over a range of temperatures
3. Melting over a range of temperatures / the broad melting range indicates the powder is a mixture (not a single compound)
4. The powder therefore cannot be used / is not the correct substance / the pharmacist should reject / not dispense the powder

## Key terms

- [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-3f923ccc) · Published by Druglandscape Ltd.