The pH of a $0.1$ molar solution of the acid $\mathrm{HQ}$ is $3$ . The value of the ionization constant, Ka…

The pH of a $0.1$ molar solution of the acid $\mathrm{HQ}$ is $3$ . The value of the ionization constant, Ka of this acid is :
  1. $3 \times 10^{-1}$
  2. $1 \times 10^{-3}$
  3. $1 \times 10^{-5}$
  4. $1 \times 10^{-7}$

Solution

$\left[\mathrm{H}^{+}\right]=\sqrt{\mathrm{K}_{\mathrm{a}} \cdot \mathrm{C}} \Rightarrow 10^{-3}=\sqrt{\mathrm{K}_{\mathrm{a}} \cdot 10^{-1}}$ $\Rightarrow \mathrm{K}_{\mathrm{a}}=10^{-5}$

Asked in: JEE Main 2012 (Offline)

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