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

The question relates to the principles of column chromatography, a technique used to separate compounds based on their adsorption to the stationary phase and their solubility in the mobile phase.

When a mixture of compounds is separated using column chromatography, the time it takes for each compound to elute is based on its interaction with the stationary and mobile phases.

1. Understanding Retention Factor (Rf): The Retention Factor (Rf) is a measure of how far a compound travels in a particular chromatographic system. It is calculated as the ratio of the distance moved by the compound to the distance moved by the solvent front.
2. Relationship between Adsorption and Rf: In column chromatography:
   • A compound with a stronger adsorption to the stationary phase will travel more slowly and have a lower Rf.
   • A compound with weaker adsorption will travel faster and have a higher Rf.
3. Analyzing the Given Information: In the question, compound 'A' eluted first. This suggests that compound 'A' is less retained by the stationary phase than compound 'B', implying that compound 'B' has a stronger adsorption.
4. Conclusion: Based on the principles of chromatography, if 'B' has eluted after 'A', it indicates that 'B':
   • Has a lower Rf value because it took longer to travel through the column due to stronger adsorption.
   • This stronger adsorption means it interacts more with the stationary phase.
5. Justification of the Correct Option: The correct answer is "
   low Rf, stronger adsorption
   ", as compound 'B' stays longer in the column due to its stronger adsorption, resulting in a lower Rf value.