A quality-control technician analyses sample T, a colouring mixture used in a cosmetic cream. Sample T is run on chromatography paper in two different solvents. The solvent front moves 8.0 cm in solvent 1 and 10.0 cm in solvent 2.
The table shows the Rf values of three reference dyes, P, Q and R, on the same type of paper in the same two solvents.
| Reference dye | Rf in solvent 1 | Rf in solvent 2 |
|---|---|---|
| P | 0.30 | 0.20 |
| Q | 0.70 | 0.60 |
| R | 0.70 | 0.40 |
Sample T gives two spots. The distances they move are:
| Spot in sample T | Distance moved in solvent 1 / cm | Distance moved in solvent 2 / cm |
|---|---|---|
| 1 | 2.4 | 2.0 |
| 2 | 5.6 | 6.0 |
Use Rf values to identify which of the reference dyes are present in sample T. Show your working.
102 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.