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Abstract
The stability constants of La(III)-formate and La(III)-propionate complexes in aqueous medium were determined by a potentiometric method using a glass electrode. The temperature was kept at 25°C and an ionic strength of 1.00 M (NaClO4) was used. Four mononuclear complexes were detected for both systems. The pKa values for the carboxylic acids (formic and propionic) were determined at the same conditions. The final values of the overall stability constants determined by a matrix solution of weighted simultaneous equations were: β1 = (13.2 ± 0.6) L mol−1, β2 = (48 ± 4) L2 mol−2, β3 = (118 ± 15) L3 mol−3, β = (85 ± 15) L4 mol4 for La(III)-formate system and β1 = (42 ± 3) L mol−1, β2 = (299 ± 25) L2 mol−2, β3 = (1201 ± 138) L3 mol−3, β4 = (2527 ± 174) L4 mol−4 for La(III)-propionate system. These data and those for La(III)/acetate from the literature were used to compare the tendency to complex.