At half-equivalence, [acid] = [salt], so [ \textpH = pK_a = -\log(1.3 \times 10^-5) = 4.89 ] (Answer: 4.89, no unit, 2 decimal places acceptable.)
The stability of complexes often relates to the "Chelate Effect." Multidentate ligands like EDTA form more stable complexes than monodentate ligands like H2Ocap H sub 2 cap O A Level H2 Chemistry 2021 Paper 3 Answers