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Q.
A certain buffer solution contains equal concentration of $X^{-}$ and $HX$ . The $K_{a}$ for $HX$ is $10^{- 8}$ . The $pH$ of the buffer is
NTA AbhyasNTA Abhyas 2022
Solution:
The Henderson equation is
$pH=pK_{a}+log \frac{\left[C o n j u g a t e \text{base}\right]}{\left[A c i d\right]}$
$=-log K_{a}+log \frac{\left[X^{-}\right]}{\left[H X\right]}$
Hence, $\left[\right.HX\left]\right.=\left[X^{-}\right]$
$=-log \left(\right.10^{- 8}\left.\right)+log 1$
or pH = 8.0.