Question

Which of the following is caused by the addition of a non-volatile solute to a solvent?

(a) Reduction in equilibrium of vapor pressure of solution

(b) Increase in melting point of the solution

(c) Decrease in the boiling point of the solution

(d) Osmosis of solute in the solution

The question was posed to me in class test.

My question is based upon Vapour Pressure of Liquid Solutions in division Solutions of Chemistry – Class 12

Answer 1

Correct answer is (a) Reduction in equilibrium of vapor pressure of solution

Explanation: This phenomenon is known as ‘relative lowering of vapor pressure’ which is a very common colligative property. When a non-volatile solute is added to a solvent, the upper surface of the solvent is covered partially. Hence, the solvent molecules do not bear maximum freedom to escape into the space as vapors. Consequently, there is a decrease in vapor pressure when compared towhat it would have been with pure solvent and no solute at all.