Certain buffer solution contains equal concentration of X- and HX. Kb for X−is 10−10. Calculate pH of buffer

$∵ K_{b (X^{-})} = 10^{- 10}$ and for conjugate acid-base pair

$K_{a (H X)} \times K_{b (X^{-})} = 10^{- 14} \Rightarrow K_{a (H X)} = 10^{- 4}$

But $\begin{aligned} [H X] = \\ (acid) = \end{aligned} \begin{matrix} [X^{-}] \\ (salt) \end{matrix}$

Now using Handerson's equation

$\begin{array}{l} ∴ p H = - \log K_{a} + \log \frac{[Salt]}{[Acid]} \\ \Rightarrow p H = - \log 10^{- 4} = 4 \end{array}$

Certain buffer solution contains equal concentration of $X^{-}$ and $HX . K_{b} for X^{-} is 10^{- 10}$ . Calculate $p H$ of buffer