Question

The freezing point depression constant $\left(K_f\right)$ of benzene is $5.12{\text{K kgmol}}^{-1}$. The depression of freezing point for the solution of molality $0.078\text{m}$ containing a non-electrolyte solute in benzene is (rounded off upto two decimal places):

• A. $0.80\text{K}$
• B. $0.40\text{K}$
• C. $0.60\text{K}$
• D. $0.20\text{K}$

Answer 1

The correct option is B $0.40\text{K}$

Depression in freezing point is given by,
$\Delta T_f=i{K}_{f}m$
Where $m=\text{molality}$
For nonelectrolyte, $i=1$
$\therefore \Delta T_f=1\times 5.12\times 0.078=0.399\text{K}\approx 0.40\text{K}$
Option (B) is correct.