Question

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

• A. 1
• B. 1.00
• C. 1.0

Answer 1

Answer: (A), (B), (C)

Molality of a solution of non volatile solute $\left(A\right)=1$
Elevation in boiling point is given by
$\Delta T_b=K_{b}m$
$3=K_b\times 1\cdots \left(1\right)$
Molality of $\left(A\right)$ in the same solvent $=2$
Depression in freezing point is given by
$\Delta T_f=K_{f}m$
$6=K_f\times 2\cdots \left(2\right)$
Dividing (1) by (2)
$\frac{K_b}{K_f}=\frac{1}{X}=\frac{1}{1}$
$\therefore X=1$