Like pure solids, liquids and gases, solutions have well-defined physical properties (e.g., vapor pressure, boiling point, etc.). A change in a property of a solvent that depends on the concentration of dissolved solute(s) particles is called a colligative property.

Colligative properties do not depend on the identity of either the solvent or the solute(s) particles (kind, size or charge) in the solution.

Colligative properties are

  1. vapor pressure lowering,
  2. boiling point elevation,
  3. freezing point lowering, and
  4. osmotic pressure.

Consider, for example, a solution prepared by dissolving 5.00 g of NaCl in 100 g of pure water at 25oC and 1 atm pressure. The following table summarizes some of the differences in the properties of pure water and the NaCl solution.

A Comparison of Some of the Properties of Pure Water and an Aqueous NaCl Solution
property pure water NaCl solution
vapor pressure 23.8 torr 23.1 torr
boiling point 100.0oC 100.8oC
freezing point 0.0oC -3.0oC
osmotic pressure 0.0 atm 33 atm