Colligative Properties of lonic solutions

when a molecule of solute e.g., sugar is dissolved in water, its physical properties are altered. The properties of dilute solutions depend on the number of solute particles in solution. The collective effect of these solute particles gives rise to colligative properties which include osmotic pressure, elevation of boiling point, lowering of vapour pressure and freezing point depression.


When ionic solutes are dissolved in water, all these properties are affected but for one difference. For example, if a mole of NaCl contains two moles of ions (Na⁺ and Cl¯), the soluble ions also exert the same influence on the solvent as do the individual molecules. Thus, in dilute Solution NaCl would be twice as effective as the sugar molecules. This led to the development of the concept of ionization, hence salts, acids or bases are more effective in lowering the freezing point because these substances are dissociated and their ions individually influence the freezing point of solvent.