STD 11 - 6.2. Equilibrium - II (icon Equilibrium) — JEE STD 11 Science — Question

From the Henderson-Hasselbalch equation

$pH = pK _{ a }+\log 10 \frac{[ A -]}{[ HA ]}$

If $\operatorname{pH}= pK _{ a } \Longrightarrow \log 10 \frac{[ A -]}{[ HA ]}=0 \Longrightarrow \frac{[ A -]}{[ HA ]}=1$

buffer exhibits the highest resistance to acid and base addition for the equimolar solution (when $pH = pKa$ ). From the plot, it is also obvious that buffer capacity has reasonably high values only for $pH$ close to $pKa$ value. The further from the optimal value, the lower buffer capacity of the solution