Organic Chemistry MCAT Practice Exam

In column chromatography, what is typically the nature of the stationary phase?

1. Non-polar

2. Polar

3. Neutral

4. Hydrophobic

The correct answer is: Polar

In column chromatography, the stationary phase is typically polar. The choice of stationary phase significantly influences the separation of compounds based on their polarity. A polar stationary phase interacts strongly with polar compounds, allowing for effective separation as non-polar compounds will elute faster due to their weak interactions with the stationary phase. In polar stationary phases, such as silica gel or alumina, the strong intermolecular forces involved with polar solvents promote the retention of polar analytes. As non-polar compounds exhibit weaker interactions, they travel through the column more quickly and elute before polar compounds. This characteristic is particularly advantageous when separating a mixture of both polar and non-polar substances, as the differing affinities for the polar stationary phase lead to effective separation based on polarity. Hence, polar is the correct characterization of the stationary phase in column chromatography.