A scientist analyses coloured substances in extract E made from berry skins. Extract E and four reference substances, K, L, M and N, are placed on the same sheet of chromatography paper in solvent 1. The experiment is repeated using solvent 2. All distances are measured from the origin line.
| Sample | Solvent 1 distance(s) / cm | Solvent 2 distance(s) / cm |
|---|---|---|
| Solvent front | 8.0 | 10.0 |
| K | 2.4 | 4.0 |
| L | 2.4 | 6.0 |
| M | 5.6 | 2.0 |
| N | 5.6 | 7.5 |
| E | 2.4 and 5.6 | 4.0 and ddd |
For extract E, the two distances listed in each solvent column are the distances travelled by its two spots. In solvent 2, the second spot from E has an Rf R_f\,Rf value of 0.75.
Calculate the distance d d\,d travelled by the second spot from extract E in solvent 2.
Which two reference substances best match the results for extract E? Explain how the results from both solvents support your answer.
Compare the movement of the first spot from extract E relative to the solvent front in the two solvents. Explain the difference.
A student concludes: ‘Extract E contains only the two reference substances you identified in part (b).’ Evaluate this conclusion.
113 exam-style questions on AQA GCSE Chemistry 8.1 Purity, formulations and chromatography, covering 8.1.1 Pure substances, 8.1.2 Formulations, and 8.1.3 Chromatography. Each one has a worked solution and a mark scheme showing where the marks go.