A chemist measures the melting points of three organic cosmetic dyes.
| Organic Dye | Melting point (°C) |
|---|---|
| A | 133 |
| B | 184 |
| C | 92 |
All of the organic dyes are pure substances.
(i) Explain what is meant by a pure substance. (ii) How can you tell that the three dyes are pure from their melting points?
The chemist uses gas chromatography to investigate a mixture of dye A and dye C.
How many peaks will the chemist see in the gas chromatogram?
The chemist then analyses dye D using thin layer chromatography.
The chromatogram is shown in the diagram below.
(i) Calculate the RfR_{\text{f}}Rf value of dye D.
Use the formula: Rf=distance travelled by substancedistance travelled by solventR_{\text{f}} = \frac{\text{distance travelled by substance}}{\text{distance travelled by solvent}}Rf=distance travelled by solventdistance travelled by substance
Give your answer to 2 decimal places. (ii) Which components are needed for thin layer chromatography?
Choose the two correct components from the list below:
- balance
- Bunsen burner
- mobile phase
- paper
- stationary phase
- thermometer
The chemist thinks that an impure dye will only have two spots on the thin layer chromatogram.
Give two reasons why the chemist is incorrect.