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?




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.


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