Question

What will be the percentage of dimerization of $61g$ of benzoic acid in $1000g$ of a solvent and producing a depression in freezing point of $2{}^{\circ }C$ ? Consider $K_f$ to be $6$ .

• A. $72\%$
• B. $67\%$
• C. $43\%$
• D. $28\%$

Answer 1

Answer: (B)

$W_{\text{benzoic acid}}=61g;$
$W_{\text{solvent}}=1000g$
$\Delta T_f=2^{\circ }C;K_f=6$
$\Delta T_f=i{K}_{f}m$
$m=\frac{61/122}{1000}\times 1000=0.5;$
$i=\frac{\Delta T_f}{k_{f}m}$
$=\frac{2}{6\times 0.5}$
$=0.67$
$\alpha =\frac{1-i}{1-1/n}$ $[\therefore n=2$ for benzoic acid]
$\alpha =\frac{1-0.67}{1-0.5}=0.66$
$=66\%$