1.8 explain how information from chromatograms can be used to identify the composition of a mixture.

The unknown mixture must be placed alongside known dyes on the same piece of paper and the chromatogram run with a suitable solvent.  The separated spots of colour in the mixture are then matched to the spots of known dyes – they will travel the same distance up the chromatography paper.

Sometimes we calculate a quantity known as the retention factor (R_f).  To do this, you measure the distance travelled by the solvent from the base line and the distance travelled by the spot of colour from the base line.

R_f  =     distance moved by coloured spot

            distance moved by solvent