# How are colligative properties determined?

##### 1 Answer
Mar 6, 2014

You determine colligative properties by making measurements.

VAPOUR PRESSURE LOWERING

The vapor pressure lowering ΔP relative to that of pure solvent A is ΔP = P_A - P.

BOILING POINT ELEVATION

To determine the boiling point, you use an apparatus like the one shown below. You heat the liquid and measure the temperature when it boils.

The boiling point elevation ΔT_b relative to that of pure solvent ${T}_{b}^{o}$ is ΔT_b = T_b – T_b^o.

FREEZING POINT DEPRESSION

To determine the freezing point, you place the solid in the apparatus shown below and warm the solid until it melts. Then you measure the temperature as it freezes.

The freezing point depression ΔT_f relative to that of pure solvent ${T}_{f}^{o}$ is ΔT_f = T_f^o – T_f.

OSMOTIC PRESSURE

You use a membrane osmometer to measure the osmotic pressure Π.