Question

The elevation in boiling point for 1 molal solution of non-volatile solute A is 3 K. The depression in freezing point for 2 molal solution of A in the same solvent is 6 K. The ratio of Kb and Kf i.e., $\frac{K_b}{K_f}$ is 1 : X. The value of X is [nearest integer]

Answer 1

Molality of a solution of non volatile solute (A) = 1

Elevation in boiling point is given by

ΔTb = Kb m

3 = Kb × 1 … (1)

Molality of (A) in the same solvent = 2

Depression in freezing point is given by

ΔTf = Kf m

6 = Kf × 2 … (2)

Dividing (1) by (2)

$\frac{K_b}{K_f}$=$\frac{1}{X}$=$\frac{1}{1}$

∴ X =1