# A student wants to find out whether a sample of aspirin tablets is pure. She measures the melting point of a small amount of the tablet and finds that it melts between 135 °C and 142 °C. The accepted melting point of pure aspirin is 140 °C. Explain what the student's melting point result tells her about the purity of the aspirin sample, and explain how a pure substance behaves differently when it melts.

> WJEC GCSE Chemistry (Wales) — 1.4 The ever-changing Earth · Explain · 4 marks

> A student measures the melting point of an aspirin tablet sample and records that it melts over the range 135 °C to 142 °C. The accepted melting point of pure aspirin is 140 °C.

## Mark scheme (4 marks)

1. The sample melts over a range of temperatures (not at a single/sharp temperature), indicating it is not pure / is a mixture.
2. A pure substance has a sharp / specific / fixed melting point (melts at one exact temperature).
3. Mixtures / impure substances melt over a range of temperatures (rather than at a single point).
4. The sample therefore contains other substances / impurities mixed with the aspirin (it is not a pure compound).

## Key terms

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

## 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-wants-to-find-out-d4c634d8) · Published by Druglandscape Ltd.