Question

The depression of freezing point of a solution of acetic acid in benzene is - ${0.2}^{\circ }C.$ If the molality of acetic acid is 0.1 m, then find the ratio of the normal mass to the abnormal mass. (Assume $K_f$ of acetic acid = ${4.0}^{\circ }C{m}^{-1}$)

• A. 1.5
• B. 0.8
• C. 0.5
• D. 0.2

Answer 1

The correct option is C 0.5

Given,
Depression in freezing point $\left(\Delta T\right)=-{0.2}^{\circ }C$
Molality of the solution (m) = 0.1 m
Freezing point depression constant $\left(K_f\right)={4.0}^{\circ }C{m}^{-1}$
Let the Van't Hoff factor = i
We know that, $\Delta T=i\times K_f\times m$
0.2 = $i\times 4\times 0.1$
$i=0.2/0.4=0.5$
Therefore, the ratio between the normal mass and abnormal mass, which is equal to the Van't Hoff factor is equal to 0.5.