Question

Two compounds I and II are eluted by column chromatography (adsorption of I > II). Which one of following is a correct statement ?

• A. I moves faster and has higher $R_f$ value than $II$
• B. II moves faster and has higher $R_f$ value than $I$
• C. I moves slower and has higher $R_f$ value than $ II$
• D. II moves slower and has higher $R_f$ value than $I$

Answer 1

The Correct Option is B

To determine which compound, I or II, moves faster in column chromatography and which has a higher retention factor (\(R_f\)), it is crucial to understand the principles of column chromatography.

Column chromatography is a method used to separate compounds based on their differential adsorption on a stationary phase and their solubility in a mobile phase. In this scenario, we have two compounds, I and II, with Compound I having a greater adsorption to the stationary phase than Compound II.

1. Since Compound I has greater adsorption to the stationary phase, it means I is more strongly retained on the stationary phase compared to Compound II.
2. Compound II, with less adsorption, will move faster through the column as it has greater interaction with the mobile phase.
3. The retention factor (\(R_f\)) is defined as the ratio of the distance traveled by the compound to the distance traveled by the solvent front on a chromatogram. Thus, a compound that moves faster through the column will typically have a higher \(R_f\) value.
4. Therefore, in this system, Compound II will move faster through the column and consequently have a higher \(R_f\) value compared to Compound I.

Based on this analysis, the correct statement is: II moves faster and has a higher \(R_f\) value than I.