Pure water has a boiling point of 100 °C and a freezing point of 0 °C. What is the boiling point and freezing point of a sample of aqueous sodium chloride?

boiling point 102°C freezing point –2°C
We shall now look at the molecular origin of the lowering of the freezing point and elevation of the boiling point. First of all, we know that the entropy of a gas is higher than the entropy of a liquid and this is higher that that of a solid. When a solid melts or a liquid vaporizes, the entropy increases and the Gibbs free energy decreases.When a solute is present, there is an additional contribution to the entropy of the liquid. Because the entropy of the liquid is already higher than that of the pure liquid, there is a weaker tendency to form the gas. The effect of this is a higher boiling point. Similarly, the enhanced molecular randomness of the solution opposes the tendency to freeze. Consequently, a lower temperature must be reached before equilibrium between solid and solution is achieved. Hence, the freezing point is lowered.