Explain4 marksStandard
A student separates three pigments extracted from a leaf using thin-layer chromatography. The stationary phase is a thin layer of aluminium oxide on a glass plate. The mobile phase is a non-polar solvent. After the run, the plate is dried and the positions of the coloured spots are recorded.
The student measures the distance moved by each pigment and the distance moved by the solvent front, and calculates the Rf value of each pigment.
Pigment A has the highest Rf value, pigment B has an intermediate Rf value, and pigment C has the lowest Rf value.
Explain why the three pigments have different Rf values.