# A food scientist is investigating whether a sample of a red food colouring is a pure substance or a mixture. She carries out paper chromatography using two different solvents, solvent A and solvent B. In solvent A the sample produces a single spot. In solvent B the sample produces three separate spots. Explain what the results from both solvents tell the food scientist about the sample, and explain how paper chromatography separates the components of a mixture.

> Eduqas A-Level Chemistry — 1.6 Kinetics · Explain · 5 marks

> A food scientist uses paper chromatography to investigate a red food colouring sample. In solvent A, the sample produces a single spot. In solvent B, the same sample produces three separate spots.

## Mark scheme (5 marks)

1. The single spot in solvent A does not confirm the sample is pure on its own / a pure compound produces a single spot in all solvents
2. The three spots in solvent B show the sample is a mixture (contains more than one compound/substance)
3. In paper chromatography the paper is the stationary phase and the solvent is the mobile phase
4. The solvent carries the substances up the paper / substances travel at different speeds through the paper
5. Separation depends on how soluble each substance is in the solvent / the more soluble a substance is in the mobile phase, the further up the paper it travels

## Key terms

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

## 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-food-scientist-is-investigating-whether-2e0f9391) · Published by Druglandscape Ltd.