COMPLEX-FORMATION EQUILIBRIA IN AQUEOUS IRON(II) ORTHOPHOSPHATE SOLUTIONS

The complex formation equilibria between iron(II) and orthophosphate ions have been studied at 25-degrees-C in 3 M Na(ClO4,H2PO4) media by measuring, with a glass electrode, the competitive reaction of H+ and Fe2+ ions for the H2PO4- species.The phosphate and iron molar concentrations ranged, respectively, from 0.03 to 1 and from 0.008 to 0.033.The potentiometric data have been explained by assuming the presence of the complexes FeH2PO4+, Fe(H2PO4)2, FeHPO4 and FeH3(PO4)2-. Equilibrium constants for their formation in the inert 3 M NaClO4 and in dilute solution are presented.