# A food scientist is investigating whether a sample of red food colouring is pure or a mixture of dyes. She uses paper chromatography to analyse the sample, then compares her results with known reference dyes. Explain how paper chromatography separates a mixture of dyes and how the scientist can use the results to determine whether the food colouring is pure.

> OCR GCSE Chemistry A: Gateway Science (J248) — C2.1 Purity and separating mixtures · Explain · 4 marks

> A food scientist is investigating a red food colouring that may contain more than one dye. She uses paper chromatography with a solvent to separate the components of the sample.

## Mark scheme (4 marks)

1. The solvent (mobile phase) moves through the paper (stationary phase), carrying the dyes with it.
2. Different dyes travel different distances because they have different distributions between the mobile phase and stationary phase / different affinities for the paper and solvent.
3. If the food colouring is pure, only one spot will be produced on the chromatogram.
4. The spots from the food colouring sample can be compared to reference dyes; if the positions match those of known dyes, the scientist can identify which dye(s) are present.

## Key terms

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

## Related

- [Revision notes for OCR GCSE Chemistry A: Gateway Science (J248)](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-is-investigating-whether-0a28ccd7) · Published by Druglandscape Ltd.