Elevation of Boiling Point – Class 12 | Chapter – 2 | Chemistry Short Notes Series PDF for NEET & JEE

Elevation of Boiling Point: Elevation of boiling point is a colligative property that occurs when a non-volatile solute is added to a solvent. It is the phenomenon in which the boiling point of a solution is higher than the boiling point of the pure solvent. The elevation of boiling point is directly proportional to the molality (number of moles of solute per kilogram of solvent) of the solution.

Elevation of Boiling Point

The elevation of boiling point can be explained by Raoult’s law, which states that the partial vapour pressure of each component in a solution is directly proportional to its mole fraction. When a non-volatile solute is added to a solvent, it decreases the mole fraction of the solvent in the vapour phase, leading to a decrease in its partial vapour pressure. This decrease in vapour pressure leads to an increase in boiling point of the solution.

The equation for calculating the boiling point elevation (ΔTb) is:

ΔTb = Kbm


  • K b is the molal boiling point elevation constant, which is a characteristic property of the solvent,
  • m is the molality of the solution.

The boiling point elevation is a useful property for determining the molecular weight of a solute. By measuring the boiling point elevation and knowing the identity of the solvent, it is possible to calculate the molar mass of the solute using the following equation:

M = (K b x w2) / (ΔTb x w1)


  • M is the molar mass of the solute
  • w2 is the mass of the solute added
  • w1 is the mass of the solvent

The boiling point elevation is also used in industrial processes, such as the production of salt from brine. In this process, the brine is heated to a temperature above its boiling point, causing the water to evaporate and leaving behind a concentrated solution of salt. The boiling point elevation allows for the production of salt at a lower temperature than would be possible with pure water, reducing energy costs and increasing efficiency.

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By Team Learning Mantras