Question

Using column chromatography, mixture of two compounds ‘A’ and ‘B’ was separated. ‘A’ eluted first, this indicates ‘B’ has

• A. high Rf , weaker adsorption
• B. high Rf , stronger adsorption
• C. low Rf , weaker adsorption
• D. low Rf , stronger adsorption

Hint:

In chromatography, the first eluted compounds are less polar with higher Rf val ues while slower moving or retained compounds are typically more polar with lower Rf values indicating stronger interaction with the stationary phase

Answer 1

The Correct Option is D

Principle of Separation: 

In column chromatography, compounds are separated based on:

• Differential adsorption: How strongly the compounds interact with the stationary phase (adsorbent).
• Solubility in the mobile phase: How easily the compounds dissolve in the solvent.

Compounds that are less strongly adsorbed to the stationary phase and more soluble in the mobile phase elute faster.

Retention Factor (\( R_f \)):

The retention factor (\( R_f \)) is defined as:

\[ R_f = \frac{\text{Distance covered by substance from base line}}{\text{Total distance covered by solvent from base line}} \]

• A higher \( R_f \) value indicates weaker adsorption (compound travels farther).
• A lower \( R_f \) value indicates stronger adsorption (compound travels a shorter distance).

Analysis of Compounds 'A' and 'B':

• Compound 'A' eluted first, meaning it has a higher \( R_f \) value and weaker adsorption to the stationary phase.
• Compound 'B' eluted later, meaning it has a lower \( R_f \) value and stronger adsorption to the stationary phase.

Conclusion:

Compound 'B' has a low \( R_f \), indicating stronger adsorption to the stationary phase.