Question

What will be $pH$ of aqueous salt solution of $AB$ if $p{K}_a$ of weak acid $HA$ is $4$ and $p{K}_b$ of weak base BOH is 5 ?

• A. $5$
• B. $7.5$
• C. $6.5$
• D. $11.5$

Answer 1

Answer: (C)

$6.5$

$BOH+HA\leftrightarrow B^{+}+A^{-}+H_{2}O$

$p^H=\frac{1}{2}{pK}_w+\frac{1}{2}{pK}_a-\frac{1}{2}{pK}_b$

$=\frac{1}{2}(14+4-5)$

$=6.5$