Henderson-Hasselbach equation:
pH = pKa + log_10 ([Ac-]/[HAc]) = pKa + log_10 (n(Ac-)/n(HAc))
Given we are only looking for the change in pH, we just need to see how "log_10 (n(Ac-)/n(HAc))" changes since pKa is constant.
Initially, log_10 (n(Ac-)/n(HAc)) = 0, as the acid and conjugate base...