# A pharmacist is checking the purity of a white solid painkiller tablet before it is approved for sale. Explain how the pharmacist could use melting point data to determine whether the active ingredient in the tablet is a pure substance or a mixture, and describe what results would be expected in each case.

> Eduqas A-Level Chemistry — 1.2 Electronic structure · Explain · 5 marks

> The pharmacist has access to a melting point apparatus and a data book listing the exact melting point of the pure active ingredient.

## Mark scheme (5 marks)

1. A pure substance has a sharp (single/specific) melting point
2. The measured melting point should be compared to the known melting point of the pure active ingredient (from the data book / reference value)
3. If the substance is pure, the melting point will match the data book value exactly / be equal to the accepted melting point of the pure active ingredient
4. A mixture melts over a range of temperatures (rather than at one fixed temperature)
5. A mixture will also melt at a lower temperature than the pure substance / the melting point of the mixture will be below the data book value

## Key terms

- [pure substance](https://www.gradenine.co.uk/glossary/pure-substance)
- [mixture](https://www.gradenine.co.uk/glossary/mixture)
- [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)
- [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-5e00c11d) · Published by Druglandscape Ltd.