Question

A $0.5$ percent solution of potassium chloride was found to freeze at $-0.24^{\circ }C$. The percentage dissociation of potassium chloride is _________(Nearest integer)
(Molal depression constant for water is $1.80Kkgmo{l}^{-1}$ and molar mass of $KCl$ is $74.6gmo{l}^{-1}$ )

Answer 1

Answer: 98

$0.5\%$ solution of $KCl$
So $m=\frac{0.5}{74.6}\times \frac{1}{0.1}$
$\Delta T_f=i\times m\times K_f$
$0.24=i\times \frac{0.5}{74.6}\times \frac{1.80}{0.1}$
$i=\frac{0.24\times 74.6}{0.5\times 1.80}\times 0.1$
$=1.989$
$1.989=1+\alpha (n-1)$
$1.989=1+\alpha$
$\alpha =.989$
$\%\alpha =98.9\%$
Ans $99\%$
If mass of $H_{2}O=99.5$
$m=\frac{0.5}{74.5}\times \frac{1}{.0995}$
$i=\frac{0.24\times 74.6\times .0995}{.5\times 1.80}$
$=1.979$
$1.979=1+\alpha (n-1)$
$1.979=1+\alpha$
$\alpha =.979$
$\%\alpha =97.9\%$
Ans $98\%$