# A scientist is testing two dye samples, P and Q, using paper chromatography with the same solvent. Dye P produces a single spot. Dye Q produces three spots. The spot from dye P travels 4.8 cm and the solvent front travels 6.0 cm. One of the spots from dye Q also travels 4.8 cm. Explain what the results tell the scientist about the nature of dye P and dye Q, and explain how the Rf value could be used to help identify the substance in dye P.

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

> A scientist uses paper chromatography to analyse two dye samples, P and Q, using the same solvent. Dye P produces a single spot that travels 4.8 cm up the paper. Dye Q produces three separate spots. The solvent front travels 6.0 cm in both cases. One of the spots in dye Q also travels 4.8 cm.

## Mark scheme (5 marks)

1. Dye P is a pure substance (single compound/element)
2. Dye Q is a mixture because it produces more than one spot
3. The Rf value for dye P is calculated as distance travelled by substance divided by distance travelled by solvent (4.8 ÷ 6.0 = 0.8)
4. The Rf value can be compared to known/reference Rf values to identify the substance in dye P
5. The substance in dye P is likely to be the same compound as the substance producing the spot at 4.8 cm in dye Q, because they have the same Rf value (in the same solvent)

## 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-scientist-is-testing-two-dye-7755b254) · Published by Druglandscape Ltd.