# A student carries out paper chromatography to investigate the pigments present in a sample of grass. After the experiment, the chromatogram shows three separate spots. Explain what can be concluded from these results, and state how the student could use the chromatogram to identify whether any of the pigments are the same as a known reference pigment.

> Cambridge International IGCSE Chemistry (0620) — 12.3 Chromatography · Explain · 4 marks

> A student crushes fresh grass leaves and dissolves the pigments in a suitable solvent. This solution is spotted onto chromatography paper and the paper is placed in a beaker containing a small depth of solvent. The solvent is allowed to rise up the paper and the paper is then removed and allowed to dry.

## Mark scheme (4 marks)

1. Three separate spots show the grass sample contains a mixture of three different pigments / substances
2. Each pigment travels a different distance up the paper because each has a different solubility in the solvent / different affinity for the paper
3. Calculate / compare the Rf value for each spot (distance travelled by spot ÷ distance travelled by solvent front)
4. If the Rf value of a spot on the chromatogram matches the Rf value of the reference pigment (run under the same conditions), then that pigment is the same as the reference

## Key terms

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

## Related

- [Revision notes for Cambridge International IGCSE Chemistry (0620)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-carries-out-paper-chromatography-4236cd5b) · Published by Druglandscape Ltd.