# A student tests two white solid substances, substance A and substance B, to find out which one is a pure substance. Substance A melts completely at 58 °C. Substance B begins to melt at 54 °C and is fully melted by 61 °C. Explain what the melting point data tells the student about the purity of each substance.

> WJEC GCSE Chemistry (Wales) — 1.3 Water · Explain · 4 marks

## Mark scheme (4 marks)

1. Substance A has a sharp melting point (melts at one specific temperature)
2. Therefore substance A is a pure substance
3. Substance B melts over a range of temperatures
4. Therefore substance B is impure / a mixture

## Key terms

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

## Related

- [Revision notes for WJEC GCSE Chemistry (Wales)](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-student-tests-two-white-solid-4271881d) · Published by Druglandscape Ltd.