Question

According to Henderson-Hasselbalch equation, when the pH of a solution becomes equal to its pKa, the solution becomes a buffer. This condition is achieved when ?

• A. The concentration of proton donor equals the concentration of proton acceptor
• B. Concentration of proton donor become zero
• C. Concentration of proton acceptor become zero
• D. The concentration of proton donor become log 1/10th of concentration of proton acceptor

Answer 1

The correct option is A The concentration of proton donor equals the concentration of proton acceptor

According to Henderson-Hasselbalch equation
$pH=(14-p{K}_b)-log\left(\frac{\left[\text{Conjugate Acid}\right]}{\text{[Base]}}\right)$ At ${25}^{o}C,p{K}_a+p{K}_b=p{K}_w=14$
$pH=p{K}_a-log\left(\frac{\left[\text{Conjugate Acid}\right]}{\text{[Base]}}\right)$
Acoording to Bronsted-Lowry, Conjugate Acid is proton donor and base is proton acceptor.
when $\text{[Conjugate Acid]}=\text{[Base]}$
$\Rightarrow \text{[Proton donor]=[Proton acceptor]}=1$
$pH=p{K}_a-log\frac{1}{1}$
$pH=p{K}_a-log1$
$pH=p{K}_a(\because log1=0)$