Buffer capacity is defined as the amount of strong acid or base the buffer can neutralize per unit change in pH, and it is influenced by:

• A. The temperature and color of the solution
• B. The concentrations of the buffer components and the closeness of the pH to the pKa
• C. The volume of solvent and the presence of salt
• D. The viscosity of the solvent and the atmospheric pressure

Answer: (B)

Buffer capacity is about how much strong acid or base a solution can neutralize with only a small change in pH. The amount of buffering species present sets the maximum amount of acid or base that can be absorbed—the larger the total concentration of the buffer components (the weak acid and its conjugate base), the greater the capacity. But capacity also depends on the pH relative to the pKa of the buffering pair. When the pH is near the pKa, the concentrations of the weak acid and its conjugate base are similar, so the buffer can react with added H+ or OH− effectively, providing strong resistance to pH changes. This is reflected in the Henderson–Hasselbalch relationship, pH = pKa + log([A−]/[HA]); near pH = pKa, [A−] ≈ [HA], enabling balanced buffering in both directions. If the pH moves far from the pKa, one form dominates and the buffer’s ability to neutralize additions in the other direction diminishes.