# A forensic scientist is investigating an ink sample found at a crime scene. The scientist uses paper chromatography to analyse the ink. Explain how paper chromatography separates the different substances in the ink sample, and describe how the scientist could use Rf values to identify the substances present.

> Edexcel GCSE Chemistry (1CH0) — 2.2 Methods of separating and purifying substances · Explain · 4 marks

> A forensic scientist uses paper chromatography to separate the components of an unknown ink sample. Several spots are produced on the chromatogram.

## Mark scheme (4 marks)

1. The solvent (mobile phase) moves through/up the paper (stationary phase), carrying the ink mixture with it
2. Substances in the ink separate because they have different solubilities in the mobile phase / travel different distances up the paper
3. The Rf value is calculated as the distance travelled by the substance divided by the distance travelled by the solvent
4. The Rf values obtained can be compared to known/reference Rf values to identify the substances present in the ink

## Key terms

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

## Related

- [Revision notes for Edexcel GCSE Chemistry (1CH0)](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-forensic-scientist-is-investigating-an-0fb3644c) · Published by Druglandscape Ltd.