Colligative properties

Definition

Colligative properties are properties of solutions that depend on the number of solute particles in a given amount of solvent, not on the nature of the solute particles. Examples include boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure.

5 Must Know Facts For Your Next Test

1. Colligative properties are independent of the chemical identity of the solute.
2. Boiling point elevation occurs when a non-volatile solute is dissolved in a solvent, raising its boiling point.
3. Freezing point depression refers to the lowering of a solvent's freezing point due to the presence of a solute.
4. Vapor pressure lowering happens because adding a non-volatile solute decreases the number of solvent molecules able to escape into the vapor phase.
5. Osmotic pressure is the pressure required to stop osmosis and is directly proportional to the molarity of the solution.

Review Questions

• What effect does dissolving a non-volatile solute have on the boiling and freezing points of a solvent?
• Why do colligative properties depend only on the number of solute particles and not their identity?
• How does adding a solute to a solvent affect its vapor pressure?

Related terms

Boiling Point Elevation: The increase in boiling point observed when a non-volatile solute is dissolved in a solvent.

Freezing Point Depression: The decrease in freezing point observed when a non-volatile solute is dissolved in a solvent.

Osmotic Pressure: The pressure needed to prevent osmosis when two solutions are separated by a semipermeable membrane.