# A pharmacist is checking the purity of two batches of a white crystalline medicine. Batch X melts sharply at 157 °C. Batch Y begins to melt at 149 °C and is not completely melted until 156 °C. Explain what the melting point data tells the pharmacist about the purity of each batch, and describe one other technique that could be used to check whether Batch Y is a pure substance or a mixture.

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

## Mark scheme (5 marks)

1. Batch X is a pure substance
2. Because Batch X has a sharp melting point (melts at a single/specific temperature)
3. Batch Y is a mixture / impure
4. Because Batch Y melts over a range of temperatures (not a sharp melting point)
5. Paper chromatography could be used — a pure substance produces a single spot in all solvents, whereas a mixture separates into more than one spot

## Key terms

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

## 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)
- [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-30c70978) · Published by Druglandscape Ltd.