Advanced Placement (AP) Chemistry Practice Exam

How does column chromatography function to separate analytes?

1. It relies on differences in molecular size

2. It uses a moving solvent to wash over a stationary phase

3. It employs temperature changes to separate components

4. It utilizes magnetic fields to isolate particles

The correct answer is: It uses a moving solvent to wash over a stationary phase

Column chromatography operates primarily through the principles of differential migration of analytes based on their interactions with both a stationary phase and a moving solvent. In this technique, a stationary phase (often a solid or a viscous liquid) is packed inside a column, and a mobile phase (the solvent) is passed through this column. As the mobile phase moves, different components of the mixture being analyzed interact with the stationary phase to varying degrees. Those that have a stronger affinity for the stationary phase will move more slowly, while those that interact less will move faster. This difference in speed leads to the separation of the components as they travel through the column. The success of column chromatography hinges on the ability to exploit the varying levels of solubility and adhesion of different substances to the stationary and mobile phases. As a result, the analytes are effectively separated as they are washed through the column by the solvent, leading to a distinct separation of the analytes over time. This process is highly effective for purifying and analyzing complex mixtures in various fields such as organic chemistry, biochemistry, and environmental science.