Paper chromatography

State which part of the chromatography paper you should draw the starting line on before adding the sample in a paper chromatography experiment.

The chromatogram below was obtained by separating a mixture of food dyes A and B. The solvent front travelled 6.0 cm from the pencil line. The diagram shows the position of the spots:

(a) State how the R_f value for dye B can be calculated. [1]

(b) Calculate the R_f value for dye B. Give your answer to two decimal places. [2]

In a paper chromatography experiment, the pencil line was drawn 1.0 cm from the bottom of the paper. The solvent front travelled 7.2 cm from the pencil line, and a blue dye moved 5.0 cm from the pencil line. Calculate the R_f value for the blue dye.

Explain why two different dyes can have the same colour but different R_f values in paper chromatography.

A student is testing three samples using paper chromatography. The chromatogram below shows the positions of the spots after the experiment was completed. The solvent front moved 9.0 cm from the pencil line.

(a) Which sample travelled furthest from the pencil line? [1]

(b) Calculate the R_f value for sample Y. [1]

(c) Explain what a high R_f value tells you about a dye's solubility in the solvent. [1]

How should you measure the distance a dye has travelled on a chromatogram to calculate its R_f value?

Describe how you would carry out a paper chromatography experiment to determine if a black ink contains more than one dye. Include three steps in your description.

A scientist measures the distance from the pencil line to the centre of a dye spot as 2.5 cm and the distance from the pencil line to the solvent front as 7.8 cm. Calculate the R_f value for this dye. Give your answer to two decimal places.