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Q.
The $pH$ of a buffer solution will be equal to the $p K_{a}$ of acid, only if
Equilibrium
Solution:
Handerson - Hasselbalch equation for acidic buffer solution is given as,
$pH = p K_{a}+\log \frac{\text { [Conjugate base }]}{[\text { Acid }]}$
Therefore, if the molar concentration of acid is equal to the molar concentration of conjugate base, we have
$pH = p K_{a}+\log 1$
Or $pH = p K_{a} [\because \log 1=0]$
Hence, $pH$ of a buffer solution becomes equal to $p K_{a}$ of acid only if,
[Acid $]=[$ Conjugate base $]$