Buffers, buffer capacity and acid–base titration curves

Learning objectives

Explain how a buffer resists pH change by consuming added strong acid or base, and write the equations for the reactions that occur when each is added

Calculate the pH of a buffer using the Henderson–Hasselbalch equation, and determine the ratio of conjugate base to weak acid required for a target pH

Explain what determines buffer capacity, and select a weak acid whose pKa is close to the desired pH when designing a buffer

Interpret a titration curve to locate the equivalence point and the half-equivalence point, determine the pKa of a weak acid, and explain why the equivalence point of a weak acid–strong base titration lies above pH 7

Compare the shapes of strong acid–strong base, weak acid–strong base and weak base–strong acid titration curves, and select a suitable indicator by matching its transition range to the pH at the equivalence point

Calculate the pH at any stated point in a titration, treating the region before the equivalence point as a buffer and the region after as excess strong acid or base