# why the buffer capacity depends on the ratio of salt and acid in acidic buffer?

According to the Henderson–Hasselbatch equation when pH = Pka for any buffer solution then why we say that this is the best buffer?

• – Loong Mar 27 '16 at 11:48

When we say it's the best buffer, we mean that the solution can resist pH change in either direction, and this occurs when $\ce{pH=pK_a}$. In the Henderson-Hasselbatch equation, $\ce{pH = pK_a + log\frac{[base]}{[acid]}}$, this is achieved as long as [base] = [acid]. The actual amounts of the acid and base forms, however, determines how far it can resist pH change.