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
$O{H^ - } > {H_2}O > C{N^ - }$
$O{H^ - } > C{N^ - } > {H_2}O$
${H_2}O > C{N^ - } > O{H^ - }$
$C{N^ - } > {H_2}O > O{H^ - }$
Values of dissociation constant, $K_a$ are given as follows
Acid | $K_a$ |
$HCN$ | $6.2\times 10^{-10}$ |
$HF$ | $7.2\times 10^{-4}$ |
$HNO_2$ | $4.0\times 10^{-4}$ |
Correct order of increasing base strength of the base $CN^-,F^-$ and $NO_2^-$ will be
The ionization constant of benzoic acid is $6.5 \times {10^{ - 5}}$ at $298$ $K$ temperature. Calculate $pH$ of its $0.15$ $M$ solution.
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