Advanced Placement (AP) Chemistry Practice Exam

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In chromatography, what does a larger retention factor (Rf) value indicate?

Stronger attraction between the solute and the solvent front
Weaker attraction between the solute and the stationary phase
Lower solubility of the solute in the solvent
Faster migration of the solute in the medium

The correct answer is: Stronger attraction between the solute and the solvent front

A larger retention factor (Rf) value in chromatography indicates a comparatively greater distance traveled by the solute relative to the solvent front. This suggests a weaker attraction between the solute and the stationary phase (the medium through which the solute is being separated). As the solute interacts less strongly with the stationary phase, it is able to move more freely and quickly with the solvent front, resulting in a higher Rf value. Therefore, the solute is more soluble in the mobile phase (the solvent), allowing it to travel further. This relationship highlights how Rf values are a critical indicator of the interactions between the solute, the solvent, and the stationary phase, which ultimately influences the separation process in chromatography.