Question

The $p{K}_a$ of a weak acid $\left(HA\right)$ is $4.5$. The $pOH$ of an aqueous buffered solution of $HA$ in which $50\%$ of the acid is ionized is

• A. 4.5
• B. 2.5
• C. 9.5
• D. 7

Answer 1

The correct option is C 9.5

For the acidic buffer solution
$pH=p{K}_a+\log \frac{\left[Salt\right]}{\left[Acid\right]}pH=4.5+\log \frac{\left[Salt\right]}{\left[Acid\right]}$
As $HA$ is $50\%$ ionized.
$\therefore \left[Salt\right]=\left[Acid\right]$
$pH=4.5\therefore pOH=14-4.5=9.5$