Which of the following is NOT a colligative property?

Concept

Colligative properties depend on the number of dissolved solute particles, not on their chemical identity.

For a dilute solution containing a non-volatile solute, the solvent vapour pressure decreases. This raises the boiling point and lowers the freezing point.

Application

Compare each named change with those consequences of adding a non-volatile solute.

Contrast

• Relative lowering of vapour pressure follows directly from the reduced escaping tendency of solvent molecules.

• Boiling point elevation occurs because the solution must be heated further to reach the external pressure.

• Freezing point depression occurs because the solution must be cooled further for the solvent to freeze.

• Elevation of freezing point has the opposite direction to the freezing-point change produced by a non-volatile solute.

Cross-check

The standard set comprises relative lowering of vapour pressure, elevation of boiling point, depression of freezing point, and osmotic pressure; an elevation of freezing point is not in this set.

Therefore, elevation of freezing point is NOT a colligative property.