Under what condition does an aqueous buffer system exhibit its maximum buffer capacity against added acid or base?
Answer and explanation
Correct answer: A. When the pH of the solution equals the pKa of the conjugate acid-base pair ([HA] = [A-])
Buffer capacity is the measure of resistance to pH change. It is maximized when the concentrations of the weak acid and its conjugate base are equimolar ([HA] = [A-]), which occurs when pH = pKa. Buffer capacity increases with higher absolute molar concentrations of the buffer components. The effective buffer range is typically pKa ± 1.
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