1.1. This question is about chromatography.

A student used paper chromatography to investigate different types of food dye.

This is the method the student used.

1. Put a spot of food colouring brand X on the start line.

2. Place spots of four separate dyes labelled A, B, C and D, on the start line.

3. Place the bottom of the paper in a beaker of water and leave it there for several minutes.

The apparatus the student used is shown in Figure 1.

Figure 1

Identify two mistakes the student made in setting up the apparatus and explain what problems the mistakes would cause.

1.2. Explain how the student could avoid these mistakes.

1.3. Another student set up the apparatus correctly and obtained a set of results which are shown in Figure 2. 

The result for sample D is not shown.

Figure 2

Calculate the R_f value of dye B, showing clearly your working out.

Give your answer to two significant figures.

1.4. The  R_f value of Dye D = 0.80. 

Use this value to calculate the distance dye D moved on the chromatography paper.

1.5. Explain how chromatography is able to separate the different dyes in sample X.