Chromatography is used to separate components of mixture which differ in their rates of ?

Analysis

The question asks for the fundamental principle behind chromatography. You need to identify the specific property that causes different components of a mixture to move at different speeds through a stationary phase when carried by a mobile phase.

Concept Explanation

Chromatography is a separation technique based on the principle of differential migration.

In chromatography, a mixture is dissolved in a fluid (the mobile phase), which carries it through a structure holding another material (the stationary phase). The components of the mixture travel at different rates because they have different affinities for the stationary phase versus the mobile phase:

• Components that have a higher affinity for the mobile phase move faster.
• Components that have a higher affinity for the stationary phase move slower.

Because they move at different speeds, they "migrate" through the system and separate over time.

Step-by-Step Solution

1. Evaluate Option A (Diffusion): Diffusion is the movement of particles from an area of high concentration to low concentration. While diffusion happens in chromatography, it is not the primary mechanism of separation.
2. Evaluate Option B (Migration): Migration refers to the movement of substances through a medium. In chromatography, the separation is specifically defined by the rate at which these substances migrate through the stationary phase. This is known as differential migration.
3. Evaluate Option C (Reaction): Chromatography is a physical separation technique, not a chemical reaction. The components do not change their chemical identity during the process.
4. Evaluate Option D (Sedimentation): Sedimentation is the process of settling particles out of a suspension, usually due to gravity or centrifugation. This is not the principle used in chromatography.

Since the components are separated based on how quickly they move (migrate) through the stationary phase, "migration" is the correct term.

Conclusion

Exam Tip: Whenever you see a question about chromatography, look for keywords like "adsorption," "partition," "stationary phase," "mobile phase," or "migration." These are the core concepts examiners test.