# A forensic scientist uses paper chromatography to compare an ink sample taken from a forged document with ink samples from three different pens, labelled P, Q and R. After running the chromatogram, the solvent front has travelled 8.0 cm. The ink from the forged document produces spots at 2.0 cm and 6.0 cm from the baseline. Pen P produces a single spot at 6.0 cm. Pen Q produces spots at 2.0 cm and 6.0 cm. Pen R produces spots at 2.0 cm, 4.5 cm and 6.0 cm. Explain how the scientist can use these results to identify which pen was used to write the forged document, and state the conclusion.

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

## Mark scheme (4 marks)

1. Spots that travel the same distance (from the baseline) in the same solvent are the same substance / component
2. The forged document ink produces two spots / is a mixture of two components
3. Pen Q produces spots at exactly the same distances (2.0 cm and 6.0 cm) as the forged document ink
4. Conclusion: pen Q was used to write the forged document / pen Q's ink matches the forged document ink

## Key terms

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

## 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)
- [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-uses-paper-chromatography-d2f28127) · Published by Druglandscape Ltd.