Question

Why does a solution containing non - volatile solute have higher boiling point than the pure solvent ? Why is elevation of boiling point a colligative property?

Answer 1

The boiling point of the solution is higher because the nonvolatile solute lowers the vapor pressure of the solvent. Thus, the temperature must be increased to a value greater than the boiling point of the pure solvent to achieve a vapor pressure equal to atmospheric pressure. This can easily understand by the concept that in a solution of non-volatile solute at the surface there are some non-volatile solute particle and some solution particle. So when heat provided there is lesser particle escaped in compare of in solution of volatile solute. So the solution has a higher boiling point.

Boiling point elevation is a colligative property because it describes how the addition of a solute will lower the boiling point of the pure solvent. Colligative properties do not depend on the identity of the solute, just the number of solute particles.