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The properties of solutions which depend on the number of solute particles and are independent of their chemical identity are called colligative properties. These are the lowering of vapour pressure, the elevation of boiling point, the depression of freezing point and osmotic pressure.

Colligative properties have been used to determine the molar mass of solutes. Solutes which dissociate in solution exhibit molar mass lower than the actual molar mass and those that associate show higher molar mass than their actual values. The extent to which a solute is dissociated or associated can be expressed in terms of Van’t Hoff factor, 'i' which is defined as the ratio of observed colligative property to the calculated colligative property.