Question

What is the effect of impurities on boiling point of water?

Answer 1

Hint: Effect of impurities on boiling point of water is an important example in colligative properties of dilute solutions.

Complete step by step answer:
Boiling point of water is defined as, “the temperature at which the vapour pressure of a liquid is equal to the pressure of the atmosphere on the liquid, i.e. 760mm”. Boiling point of water is 100 degree Celsius at mean sea level.
Boiling point is related to the vapour pressure of the solution. On adding an impurity, the vapor pressure of solution decreases. With an increase in concentration of solute, vapour pressure decreases, hence boiling point increases.
This phenomenon is known as ‘elevation of boiling point’. For example – adding salt to water will lead to increase in its boiling point.
The elevation of boiling point is directly proportional to lowering of vapour pressure. It is given by the formula –
\[\text{ }\!\!\Delta\!\!\text{ }{{\text{T}}_{\text{b}}}\text{= }\!\!\mu\!\!\text{ }{{\text{p}}^{\text{0}}}\text{-p}\] , where \[\text{ }\!\!\Delta\!\!\text{ }{{\text{T}}_{\text{b}}}\]is the elevation of boiling point.
In short, we can say that adding impurities to water leads to increase in its boiling point.

Note: Colligative properties are those properties of dilute solutions containing non-volatile solute which depend only on the concentration and not on the nature of solute particles, in other words, number of particles of solute present in the solution. Colligative property includes –
1) Lowering of vapour pressure of solvent
2) Osmotic pressure of the solution
3) Elevation of boiling point of solvent
4) Depression of freezing point of the solvent.