Question

The freezing point of benzene decreases by ${0.45}^{\circ }C$ when 0.2 $g$ of acetic acid is added to 20 $g$ of benzene. If acetic acid associates to form a dimer in benzene, percentage association of acetic acid in benzene will be:
$(K_{f}forbenzene=5.12Kkgmo{l}^{-1})$

• A. $80.4\%$
• B. $74.6\%$
• C. $94.4\%$
• D. $64.6\%$

Answer 1

The correct option is C $94.4\%$

$\Delta T_f=i\times K_f\times m$

$\Rightarrow 0.45=i\times 5.12\times \frac{0.2\times 1000}{60\times 20}$

$i=0.527$

$2C{H}_{3}COOH\rightleftharpoons (C{H}_{3}COOH{)}_2$

$1-\alpha$ $\frac{\alpha }{2}$

$i=1-\alpha +\frac{\alpha }{2}$

$\alpha =0.946$

$\therefore \%$ dissociation is $94.6\%$