Freezing point depression

Definition

Freezing point depression is the decrease in the freezing point of a solvent when a solute is added. It is a colligative property, meaning it depends on the number of solute particles rather than their identity.

5 Must Know Facts For Your Next Test

1. Freezing point depression occurs because solute particles disrupt the formation of the solid lattice structure of the solvent.
2. The magnitude of freezing point depression is directly proportional to the molal concentration of the solute.
3. The formula for freezing point depression is $\Delta T_f = i \cdot K_f \cdot m$, where $i$ is the van 't Hoff factor, $K_f$ is the cryoscopic constant, and $m$ is the molality of the solution.
4. Electrolytes cause a greater freezing point depression than nonelectrolytes due to their dissociation into multiple particles.
5. Common applications include using salt to melt ice on roads and adding antifreeze to car radiators.

Review Questions

• What effect does adding a solute have on the freezing point of a solvent?
• How does an electrolyte differ from a nonelectrolyte in terms of freezing point depression?
• Write and explain the formula used to calculate freezing point depression.

Related terms

Colligative Properties: Properties that depend on the number of solute particles in a solution but not on their nature.

Boiling Point Elevation: The increase in boiling point of a solvent upon addition of a non-volatile solute.

Molality: A concentration unit defined as moles of solute per kilogram of solvent.