Effect of pH
pH changes will influence complex formation when any of the species involved has Brønsted acidity or basicity. Several good ligands (apart from Cl-, Br- and I-) are basic and protonation at low pH will be compete with complex formation. This is significant in analytical applications. For instance, in titrations with EDTA, Fe3+ (in which K1 is around 1025) can be titrated at a pH down to two, however with Ca2+ (in which K1 is about 1010) a pH of minimum seven is needed because at lower pH values complex formation is not complete.