A manufacturer keeps a standard sample of the colouring mixture used in a cleaning product. A chemist checks three new batches, L, M and N, against the standard. Each sample is run on the same type of chromatography paper, first with solvent A and then with solvent B.
| Sample | Rf values with solvent A | Rf values with solvent B |
|---|---|---|
| Standard | 0.34 and 0.69 | 0.21 and 0.57 |
| Batch L | 0.34 and 0.69 | 0.21 and 0.57 |
| Batch M | 0.34 and 0.69 | 0.21 and 0.74 |
| Batch N | 0.34 and 0.52 | 0.21 and 0.57 |
A batch must be rejected if it does not contain the same colourings as the standard.
Which batch or batches must be rejected?
Batch M only
None of the batches
Batches M and N only
Batch N only
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.