Question

In chromatography, which of the following statements is incorrect for ${R_f}$ ?
(A) ${R_f}$ value depends on the type of chromatography
(B) The value of ${R_f}$ cannot be more than one
(C) Higher ${R_f}$ value means higher adsorption
(D) ${R_f}$ value is dependent on mobile phase

Answer 1

. ${R_f}$ value is the retardation factor or retention factor of the solute in chromatography. It depends upon the type of chromatography, nature of solute and mobile phase and nature of stationary phase.

Complete step by step answer:
The ${R_f}$ value stands for retardation factor in chromatography.
- Retardation factor is the ratio of distance travelled by the center of the spot to the solvent front. So, we can write for the retardation factor that
${R_f} = \dfrac{{{\text{Distance travelled by spot}}}}{{{\text{Distance travelled by solvent front}}}}$

- Sometimes, retardation factor is also called retention factor as well.
- We can say that as the type of chromatography changes, the value of retardation factor also changes. We know that there are many types of chromatography like paper chromatography, column chromatography, etc..
- Here the distance travelled by the spot cannot be more than the distance travelled by the solvent front. Thus, we can say that the value of ${R_f}$ is always less than 1.
- We can say that if the ${R_f}$ value is higher, then it would have covered more distance. That means that the absorption of the solute is less here. Thus, the statement given in option (C) is not true.
- In different mobile phases, the distance covered by the spot of solute is different. Thus, the ${R_f}$ values are also different.
So, the correct answer is “Option C”.

Note: Remember that the solute which has the higher value of ${R_f}$ will come out first in the separation of mixtures of solutes. The solute with the least ${R_f}$ value will come out last in the separation of the mixture of solutes with chromatography.