If a $0.1 \mathrm{M}$ solution of HCN is $0.01 \%$ ionised, the ioniation constant for $\mathrm{HCN}$ is

If a $0.1 \mathrm{M}$ solution of HCN is $0.01 \%$ ionised, the ioniation constant for $\mathrm{HCN}$ is
  1. $10^{-3}$
  2. $10^{-5}$
  3. $10^{-7}$
  4. $10^{-9}$

Solution

$C=0.1 \mathrm{~m} \quad \alpha \%=0.01$
$\alpha=\frac{0.01}{100}=1 \times 10^{-4}$
$\mathrm{~K}=\mathrm{C} \alpha^{2}=0.1 \times\left(1 \times 10^{-4}ight)^{2}$
$=1 \times 10^{-9}$

Asked in: JEE-TOPICTESTS-CHEMISTRY

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