A student uses paper chromatography to find out which dyes are in food colouring E.
The table shows the Rf values of the spots from E and from four dyes, 1 to 4. All the samples were run on the same paper with the same solvent.
| Substance | Rf value of each spot |
|---|---|
| E | 0.21 and 0.64 |
| Dye 1 | 0.21 |
| Dye 2 | 0.45 |
| Dye 3 | 0.64 |
| Dye 4 | 0.83 |
Which dyes are in food colouring E?
Dye 3 only
Dyes 1 and 3 only
Dyes 2 and 4 only
Dyes 1, 2 and 3 only
51 exam-style questions on OCR GCSE Chemistry 2.1 Purity and separating mixtures, covering 2.1.1 Pure substances and melting point data, 2.1.2 Relative formula mass and empirical formula, 2.1.3 Formulations as useful mixtures, 2.1.4 Techniques for separating mixtures, and 2.1.5 Chromatography and Rf values. Each one has a worked solution and a mark scheme showing where the marks go.