Organic Chemistry Basics Result Question 4
4. In chromatography, which of the following statements is incorrect for $R _f$ ?
(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
(2019 Main, 10 April II)
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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. $R _f$ 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.
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