Question

DUPLICATE. 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 [HA] = [A-] and pH = pKa 

if Ka is 5.2e-5 then pKa = pH = 4.28