Question

In a buffer solution containing equal concentration of $B^{-}$and $HB$, the $K_{b}$ for $B^{-}$is $10^{-10}$. The $pH$ of buffer solution is

• A. 10
• B. 7
• C. 6
• D. 4

Answer 1

Answer: (D)

(i) For basic buffer,
$p O H=p K_{b}+\log \frac{[\text { salt }]}{[\text { base }]}$
(ii) $p H+p O H=14$
Given, $K_{b}=1 \times 10^{-10},[$ salt $]=[$ base $]$
$p O H=-\log K_{b}+\log \frac{[\text { salt }]}{[\text { base }]} $
$\therefore p O H=-\log \left(1 \times 10^{-10}\right)+\log 1=10 $
$p H+p O H=14\left[\because \text { concentration of }\left[B^{-}\right]=[H B]\right.$
$p H=14-10=4$