Partition coefficients
Partition coefficients
- Shake a solute with two solvents that don't mix — it spreads between them.
- The ratio of its concentrations is the partition coefficient.
- Polarity decides which solvent it prefers.
The partition coefficient
$$K_{\text{pc}} = \frac{[\text{solute in solvent 1}]}{[\text{solute in solvent 2}]}$$
- It is constant at a fixed temperature.
- It only applies when the solute is in the same physical state in both solvents.
Practice
The partition coefficient is:
Kpc = [solute in solvent 1] / [solute in solvent 2], constant at a fixed temperature.
Practice
The partition coefficient applies only when the solute is:
Kpc is valid when the solute exists in the same physical state in each solvent.
Polarity decides
- The value depends on the polarity of the solute and each solvent.
- A non-polar solute dissolves more in the non-polar solvent; a polar solute prefers the polar solvent.
Practice
A non-polar solute will dissolve more in:
"Like dissolves like": a non-polar solute prefers the non-polar solvent; a polar solute the polar one.
Practice
The value of the partition coefficient depends on the polarity of the solute and solvents.
Polarity governs how the solute distributes, so it sets the partition coefficient.
You've got it
Key idea
- $K_{\text{pc}} = \dfrac{[\text{solute in solvent 1}]}{[\text{solute in solvent 2}]}$ (constant at fixed temperature)
- it applies when the solute is in the same physical state in both solvents
- non-polar solute → non-polar solvent; polar solute → polar solvent