# A student uses paper chromatography to analyse a sample of food colouring. The chromatography is run using water as the solvent. The student then runs the same food colouring sample using ethanol as the solvent. Explain how paper chromatography separates the components of a mixture, and suggest why the two solvents may produce different results for the same food colouring sample.

> OCR A-Level Chemistry B: Salters (H433) — 6.3 Analysis (chromatography, NMR) · Explain · 5 marks

> Paper chromatography is a technique used to separate and identify the different components in a mixture. A sample is placed on the baseline of chromatography paper and a solvent is allowed to travel up the paper. Different components travel different distances up the paper.

## Mark scheme (5 marks)

1. The solvent moves up the chromatography paper carrying the components of the mixture with it
2. Components that are more soluble in the solvent / attracted more to the solvent travel further up the paper
3. Components that are more attracted to / more strongly held by the paper (stationary phase) travel less far
4. Different components have different solubilities in different solvents, so the Rf values / distances travelled will differ between water and ethanol
5. A different solvent may be able to separate components that appeared as one spot with the other solvent / may reveal components not separated by water

## Key terms

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

## Related

- [Revision notes for OCR A-Level Chemistry B: Salters (H433)](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-student-uses-paper-chromatography-to-813eae6c) · Published by Druglandscape Ltd.