A quality-control chemist used paper chromatography to identify a colouring in a tablet coating. The sample of colouring was labelled C.
For solvent 1, all positions were measured upwards from the bottom edge of the chromatography paper.
| Position measured | Distance from the bottom edge in mm |
|---|---|
| Origin line | 18 |
| Centre of the spot from sample C | 62 |
| Solvent front | 86 |
Using solvent 2, sample C had an Rf R_f\,Rf value of 0.40.
Three reference colourings were tested using the same solvents and the same type of chromatography paper.
| Reference colouring | Rf R_f\,Rf in solvent 1 | Rf R_f\,Rf in solvent 2 |
|---|---|---|
| P | 0.65 | 0.40 |
| Q | 0.65 | 0.72 |
| R | 0.79 | 0.40 |
Calculate the Rf R_f\,Rf value of sample C in solvent 1.
Use the equation:
Rf=distance moved by the substancedistance moved by the solventR_f = \dfrac{\text{distance moved by the substance}}{\text{distance moved by the solvent}}Rf=distance moved by the solventdistance moved by the substance
Use the results for both solvents.
Give the letter of the reference colouring that could be sample C.
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.