Question

75.2 g of $C_6{H}_{5}OH$ is dissolved in 1 kg of solvent of $K_f=14Kmola{l}^{-1}$. If the depression in freezing point is 7 K and the percentage of phenol that dimerises is x%, find the value of x.

Answer 1

$\Delta T_f=K_{f}im\Rightarrow 7=14im\Rightarrow im=0.5$
$2PhOH\rightleftharpoons (PhOH{)}_2$
$1-\alpha$ $\frac{\alpha }{2}$
$i=1-\frac{\alpha }{2}$
$im=(1-\frac{\alpha }{2})\frac{75.2}{94}=0.5\Rightarrow 1-\frac{\alpha }{2}=0.5\times \frac{94}{75.2}=0.625\Rightarrow \alpha =0.75=75\%$