A scientist tests an unknown white powder, U, using thin layer chromatography in two different solvents.
The table shows the Rf values of four known substances in each solvent.
| Substance | Rf value in solvent 1 | Rf value in solvent 2 |
|---|---|---|
| J | 0.42 | 0.71 |
| K | 0.42 | 0.35 |
| L | 0.60 | 0.71 |
| M | 0.15 | 0.35 |
U gives one spot in each solvent.
In solvent 1, the spot moves 2.1 cm and the solvent front moves 5.0 cm.
In solvent 2, the spot moves 2.8 cm and the solvent front moves 8.0 cm.
Which substance is U?
J
K
L
M
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.