SALT EFFECTS ON THE PROTONATION OF ORTHO-PHOSPHATE BETWEEN 10-DEGREES-C AND 50-DEGREES-C IN AQUEOUS-SOLUTION - A COMPLEX-FORMATION MODEL

Protonation constants of o-phosphate were studied potentiometrically, using the (H+)-glass electrode in aqueous NaCl, KCl and tetraethylammonium iodide solutions, at 0 less-than-or-equal-to I less-than-or-equal-to 1M and 10 less-than-or-equal-to T less-than-or-equal-to 50-degrees-C. The differences found in the protonation constants for different salt solutions are explained by a complex formation model. The formation of the species MPO4(2-), MHPO4-, MH2PO4(0), M2PO4- and M2HPO4(0) (M = Na+, K+) is hypothesized. In mixed NaCl-KCl solutions, it is possible to find the mixed metal species NaKPO4- and NaKHPO4(0). Ionic strength and temperature dependence parameters are reported for all species. The relevance of Na+ and K+ complexes is discussed in connection with speciation problems of natural fluids, such as marine water and urine.