Which separation technique is used to separate different pigments in a mixture based on their affinity for a stationary phase and a mobile phase?

1. Analyze the question

The question asks for a specific separation technique that relies on the movement of components (pigments) through a system involving two phases: a stationary phase (which stays still) and a mobile phase (which moves).

2. Explain the concept

This process is based on the principle of differential migration. In a mixture, different components have different chemical properties (such as polarity or solubility).

• Stationary Phase: A solid or liquid supported on a solid that remains fixed in place.
• Mobile Phase: A solvent or gas that flows through the stationary phase, carrying the mixture with it.

As the mobile phase moves, the components of the mixture travel at different speeds depending on how strongly they "stick" to the stationary phase versus how well they dissolve in the mobile phase. This causes the pigments to separate into distinct bands or spots.

3. Show the solution

• Filtration: Used to separate an insoluble solid from a liquid (e.g., sand from water). It does not involve a mobile/stationary phase interaction.
• Decantation: Used to separate a liquid from a settled solid by pouring off the top layer. It is a mechanical separation, not based on phase affinity.
• Distillation: Used to separate components of a mixture based on differences in their boiling points.
• Chromatography: Specifically designed to separate mixtures by distributing the components between a stationary phase and a mobile phase. This is the standard method used in laboratories to separate plant pigments (like chlorophyll and carotenoids).

4. Identify the answer

Based on the principles of separation science, the technique described is Chromatography.

5. Exam Tip

Think of chromatography as a "race." The pigments are the runners. The stationary phase is the track, and the mobile phase is the wind pushing them. Some pigments are "heavier" or "stickier" (high affinity for the stationary phase) and move slowly, while others are "lighter" or more soluble in the solvent (high affinity for the mobile phase) and move quickly. This difference in speed is what separates them!