Q. The $pK_{a}$ of a weak acid ($HA$) is 4.5. The $pOH$ of an aqueous buffered solution of $HA$ in which 50% of the acid ionised is
A) 4.5
B) 2.5
C) 9.5
D) 7.0
Explanation
(c)
From the aqueous buffered solution of $HA$, 50% HA is ionised
[$HA$]$= \lbrack A^{-}\rbrack$
Buffer solution of weak acid $HA \longrightarrow$ acidic buffer
$pH = pK_{a} + \log\frac{\lbrack A^{+}\rbrack}{\lbrack HA\rbrack}$
or $pH = pK_{a} = 4.5$
$pOH = pK_{w} - pH$
$pOH = 14 - 4.5 = 9.5$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.