Given

$(i)$ $\begin{gathered}
  HCN\left( {aq} \right) + {H_2}O\left( l \right) \rightleftharpoons {H_3}{O^ + }\left( {aq} \right) + C{N^ – }\left( {aq} \right) \hfill \\
  {K_a} = 6.2 \times {10^{ – 10}} \hfill \\ 
\end{gathered} $

$(ii)$ $\begin{gathered}
  C{N^ – }\left( {aq} \right) + {H_2}O\left( l \right) \rightleftharpoons HCN\left( {aq} \right) + O{H^ – }\left( {aq} \right) \hfill \\
  {K_b} = 1.6 \times {10^{ – 5}} \hfill \\ 
\end{gathered} $

These equilibria show the following order of the relative base strength

${K_a}$ of $C{H_3}COOH$ is $1.76 \times {10^{ – 5}}$ at $298$ $K$ temperature. Calculate dissociation constant of its conjugate base.

$pH$ of an aqueous solution $H_2CO_3$ is $3.3$. If ${K_{{a_1}}} = {10^{ – 3}}$and ${K_{{a_2}}} = {10^{ – 13}}$ then $[HCO_3^-]$ is

A weak base $MOH$ of $0.1\,N$ concentration shows a $pH$ value of  $9$ . What is the percentage degree of ionization of the base ? …….$\%$

Write characteristics and uses of ${K_a}$ value.