Rapid Review

Colligative Properties

A colligative property is any property that depends on the concentration of solute particles in a solution but not on their identity. Colligative properties only apply to solutions.
Raoult's Law

P = mole fraction of solvent x Po

where P is the partial pressure of solvent vapor from a solution, Po is the partial pressure of vapor from pure solvent, and the mole fraction of the solvent is concentration of solvent particles / concentration of all particles in a solution.

(Note: Vapor pressure is the pressure of a gas that collects above a liquid in a closed container. The gas and the liquid are in dynamic equilibrium.)

DP = mole fraction of solute x Po

Boiling Point Elevation

In dilute solutions, DT_BP = k_b x molality of solute particles
where k_b is the molal B.P. elevation constant

Freezing Point Depression

DT_FP = -k_f x molality of solute particles
where k_f is the molal freezing point depression constant

Osmotic Pressure

The osmotic pressure of a solution is the minimum pressure needed to prevent osmosis of pure water across a semipermeable membrane into this solution.

Osmotic pressure = RT [solute particles]