# A scientist is testing two samples of a soluble white solid. Sample A is known to be pure aspirin. Sample B is suspected to be impure. Explain how the scientist could use melting point data to determine whether Sample B is pure or impure, and describe what results would be expected for each sample.

> Eduqas A-Level Chemistry — 1.3 Chemical bonding · Explain · 5 marks

> Aspirin is a medicine that can be produced in a laboratory. A pure substance has a sharp, specific melting point, whereas a mixture melts over a range of temperatures.

## Mark scheme (5 marks)

1. A pure substance melts at a specific/sharp temperature (not a range)
2. Sample A (pure aspirin) would melt at a single, sharp temperature
3. A mixture / impure substance melts over a range of temperatures
4. Sample B (if impure) would melt over a range of temperatures (lower than the true melting point of pure aspirin)
5. The melting point of Sample B can be compared to the known melting point of pure aspirin (Sample A) to confirm purity

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Chemistry](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-scientist-is-testing-two-samples-98238858) · Published by Druglandscape Ltd.