Question

A student chromatographs a mixture and after developing the spots with a suitable reagent he observes the following

Answer 1

Rf value is the ratio of the distance traveled by the solute to that of the solvent front on the paper used in chromatographic separation.

From the image it is clear the distance traveled by solvent front = 7.3 cm

Distance traveled by the component -1 of the mixture = 1.4 cm

Distance traveled by the component -2 of the mixture = 3.0 cm

Distance traveled by the component -3 of the mixture = 4.5 cm

Distance traveled by the component -4 of the mixture = 6.5 cm

Rf value of component-1 = $\frac{1.4 cm}{7.3 cm} =0.192$

Rf value of component-2 = $\frac{3.0 cm}{7.3 cm} =0.410$

Rf value of component-3 = $\frac{4.5 cm}{7.3 cm} =0.616$

Rf value of component-4 = $\frac{6.5 cm}{7.3 cm} =0.890$

b) Samples can be separated from a mixture using chromatography as the relative affinities for the compounds towards the paper (stationary phase) and the solvent(mobile phase) are different. Each component spends different amounts of time on the stationary phase depending on it chemical nature. So, the components in a mixture can be separated based on their polarities and relative degrees of adsorption on the stationary phase.