# A student investigates whether a sample of aspirin is pure. She measures the melting point of the aspirin sample and finds that it melts between 132 °C and 141 °C. The melting point of pure aspirin is 135 °C. Explain what the student's results tell her about the purity of the aspirin sample, and describe how melting point data can be used to identify whether a substance is pure.

> WJEC A-Level Chemistry (Wales) — 1.5 Energetics · Explain · 5 marks

> A student investigates whether a sample of aspirin is pure. She measures the melting point of the aspirin sample and finds that it melts between 132 °C and 141 °C. The melting point of pure aspirin is 135 °C.

## Mark scheme (5 marks)

1. A pure substance melts at a specific/sharp (single) temperature
2. A mixture melts over a range of temperatures
3. The aspirin sample is impure / is a mixture (because it melts over a range of temperatures)
4. The measured melting point range can be compared to the known melting point of a pure substance to identify it
5. If the measured melting point is sharp and matches the known value, the substance is confirmed as pure / correctly identified

## Key terms

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

## Related

- [Revision notes for WJEC A-Level 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-investigates-whether-a-sample-ce291954) · Published by Druglandscape Ltd.