Question

The half-equivalence point of a titration occurs half way to the end point, where half of the analyte has reacted to form its conjugate, and the other half still remains unreacted. If 0.580 moles of a monoprotic weak acid (Ka = 4.5 × 10-5) is titrated with NaOH, what is the pH of the solution at the half-equivalence point?

Answer 1

At the half-equivalence point, [A–] = [HA] and so [A–]/[HA] = 1, which is true regardless of the initial amount of acid. Use the Hernderson- HASSELBACH EQ.