Organic Chemistry Basics 2 Question 4
4. In chromatography, which of the following statements is incorrect for $R_{f}$ ?
(2019 Main, 10 April II)
(a) $R_{f}$ value depends on the type of chromatography
(b) Higher $R_{f}$ value means higher adsorption
(c) $R_{f}$ value is dependent on the mobile phase
(d) The value of $R_{f}$ can not be more than one
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Answer:
Correct Answer: 4. (b)
Solution:
- In chromatography, the expression of retention factor $\left(R_{f}\right)$ is
$$ R_{f}=\frac{\text { Distance travelled by the compound from origin }}{\text { Distance travelled by the solvent from origin }}<1 $$
The value of $R_{f}$ signifies the relative ratio of migration of each component of the mixture with respect to the developing solvent used. $\quad R_{f}$ value depends on the type of adsorption chromatography like TLC (Thin-Layer Chromatography), paper chromatography etc. The $R_{f}$ value is also the characteristic of a compound (sample) for a given developing solvent at a given temperature.
When the compound in the sample (usually less polar) is weakly adsorbed the spot will travel a shorter distance from the origin and hence the $R_{f}$ value will be decreased.
