2. A drop of the unknown solution is applied 2.0 cm from the bottom edge of a pi

Question

2. A drop of the unknown solution is applied 2.0 cm from the bottom edge of a piece of chromatography paper. In the developed chromatogram the solvent front is located 92 mm from the bottom edge and a component from an analyzed sample is located 65 mm from the bottom edge. What is the Rf value for the component?

3.A piece of paper is spotted with a solution containing a mixture of two components, A and B. The chemical affinity of A for the stationary phase is greater than that of B, and the chemical affinity of A for the mobile phase is less than of B. Which substance will have the larger Rf value? Explain your answer.

Explanation / Answer

2)

Rf value represents the ratio between the migration distance of a substance and the migration distance of the solvent front

Rf is the ratio of migration distane of substance to the migration distance of solvent front

Rf = distance of substance migration / distance of solvent migration

       = 65-2 / 92-2

        = 63/90 = 0.7 is the Rf value for the component

3)

The chemical affinity of A for the stationary phase is greater than that of B, and the chemical affinity of A for the mobile phase is less than of B

so since the compound will move with the solvent or mobile phase .and there will be interaction of compound with mobile phase and stationary phase.

if the compound has higher affinity for stationary phase then the interaction of compound with stationary phase will more and hence it migration over the stationary phase will be low .

so higher the affinity of compount with stationary phase lesser will be migration distance .and hence lower the Rf value

so the component B will have higher Rf value than A as its affinity of B for stationary phase is less than A

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