This question is about chromatography of food colouring - AQA - GCSE Chemistry Combined Science - Question 3 - 2019 - Paper 2

In paper chromatography, dyes are distributed differently between the stationary and mobile phases. This happens because different dyes have different solubilities, leading to varying forces of attraction to the stationary phase (the paper) and the mobile phase (the solvent). As a result, the dyes move up the paper at different speeds or rates.

Because chromatograms have different dots or colours, one can observe various spots on the chromatogram in a vertical column, indicating the presence of multiple dyes.

To identify unknown dyes, the student can run known dyes and food colouring as a chromatogram, comparing the distances moved or the R values. This way, they can identify which unknown dyes are present by comparing their R values to known standards.