# A food scientist tests two samples of a red food colouring. Sample A is a known pure compound. Sample B is a food colouring product bought from a shop. Both samples are analysed using paper chromatography with the same solvent. Sample A produces one spot and Sample B produces three spots. Explain what these results tell the scientist about the two samples, and describe the role of the mobile phase in separating the substances in Sample B.

> WJEC GCSE Chemistry (Wales) — 1.2 Atomic structure and the periodic table · Explain · 4 marks

## Mark scheme (4 marks)

1. Sample A is a pure substance / contains only one compound
2. Sample B is a mixture / contains more than one compound
3. The mobile phase (solvent) carries the substances / mixture up the paper
4. Substances in Sample B travel different distances because they have different solubilities in the mobile phase / solvent

## Key terms

- [mobile phase](https://www.gradenine.co.uk/glossary/mobile-phase)
- [paper chromatography](https://www.gradenine.co.uk/glossary/paper-chromatography)

## 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-food-scientist-tests-two-samples-52f28a6b) · Published by Druglandscape Ltd.