Question

A certain buffer solution contains equal concentration of $X^{-}$ and $HX$. The $K_b$ for $X^{-}$ is $10^{-10}$ . The pH of the buffer is

• A. 4
• B. 7
• C. 10
• D. 14

Answer 1

Answer: (A)

$K_a(HX)=\frac{k_w}{K_b}=10^{-4}$
$pH=p{K}_a+\log \frac{[X^{-}]}{[HX]}$
$\Rightarrow p{K}_a=4$ $[\because [X^{-}]=[HX]]$