# A student carries out paper chromatography on two samples, sample A and sample B, using the same solvent. Sample A produces a single spot that travels 4.8 cm from the baseline. The solvent front travels 6.0 cm from the baseline. Sample B produces three separate spots that travel 1.5 cm, 3.0 cm and 4.8 cm from the baseline. Explain what these results tell the student about the nature of sample A and sample B, and calculate the Rf value of the spot in sample A, stating what this value could be used for.

> Eduqas A-Level Chemistry — 1.7 Equilibria · Explain · 5 marks

> Paper chromatography is used to separate and identify substances in a mixture. The Rf value of a substance is calculated as the distance travelled by the dissolved substance divided by the distance travelled by the solvent.

## Mark scheme (5 marks)

1. Sample A is a pure substance because it produces only a single spot
2. Sample B is a mixture because it produces more than one spot
3. The Rf value of the spot in sample A is 0.8
4. The Rf value can be used to identify the substance in sample A
5. The substances in a mixture separate because they have different solubilities in the mobile phase / solvent, so they travel different distances up the paper

## Key terms

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

## 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-student-carries-out-paper-chromatography-1b1d9022) · Published by Druglandscape Ltd.