An environmental scientist uses thin layer chromatography to analyse coloured substances removed from wastewater.
The same stationary phase is used for every plate.
In ethanol, a spot produced by substance X moves 3.75 cm when the solvent moves 7.50 cm.
In a repeat using ethanol, the solvent moves 6.4 cm.
Calculate the distance substance X should move. Give your answer in cm.
The table describes how substances Y and Z are distributed during chromatography.
| Solvent | Substance Y | Substance Z |
|---|---|---|
| water | spends more time held on the stationary phase | spends more time dissolved in the mobile phase |
| ethanol | spends more time dissolved in the mobile phase | spends more time held on the stationary phase |
Predict which substance forms the spot further from the start line in each solvent.
Explain your predictions.
The scientist wants to choose a solvent for checking whether four substances, J, K, L and M, are present in unknown wastewater samples.
Each pure substance is analysed on a separate plate using water.
| Substance | Distance moved by solvent / cm | Distance moved by spot / cm |
|---|---|---|
| J | 8.0 | 2.0 |
| K | 7.2 | 1.8 |
| L | 9.0 | 4.5 |
| M | 8.5 | 6.8 |
The analysis is repeated using ethanol.
| Substance | Distance moved by solvent / cm | Distance moved by spot / cm |
|---|---|---|
| J | 7.5 | 1.5 |
| K | 8.0 | 3.2 |
| L | 9.0 | 5.4 |
| M | 8.5 | 6.8 |
The scientist concludes, "Ethanol is the best solvent for checking whether all four substances are present."
Evaluate this conclusion. Use the data from both solvents.
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.