Solubility of sodium oxalate in concentrated Eeectrolyte solutions

The solubility of solid sodium oxalate (Na2Ox) has been measured in a variety of concentrated aqueous electrolyte solutions at T = 298.15, 323.15, and 343.15 K by titration of dissolved oxalate with permanganate. The electrolyte solutions studied (not necessarily at all temperatures) were NaCl, NaClO4, NaOH, LiCl, KCl, Me4NCl, and KOH at concentrations ranging from approximately 0.5 mol·kg–1 to at least 5 mol·kg–1. Where comparisons were possible, the present results were in excellent agreement with literature data. The solubility of Na2Ox(s) decreased markedly with increasing concentrations of Na+(aq), due to the common ion effect. This decrease was almost independent of the electrolyte anion. A number of ternary mixtures of these electrolytes were also investigated at constant ionic strength. Consistent with the binary mixtures, the solubility of Na2Ox(s) showed almost no dependence on solution composition at constant Na+(aq) concentrations. Solubilities in non-Na+ media, with the exception of Me4NCl, showed small but regular increases with increasing concentration of added electrolyte, probably reflecting activity coefficient variations. The solubility data in certain Na+-containing media could be correlated accurately at all temperatures and concentrations using a relatively simple Pitzer model with interaction parameters for Na2Ox(aq) assumed to be identical to those available in the literature for Na2SO4(aq).