Solubility of Sodium Oxalate in Concentrated Electrolyte Solutions

Abstract

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).

Salt Solubilities in Aqueous Solutions of NaNO3, NaNO2, NaCl, and NaOH: A Hofmeister-like Series for Understanding Alkaline Nuclear Waste

“… Comparison of Na 2 C 2 O solubility in the Hanford waste to simple NaNO 3 and NaOH solutions (data from TWINS database as well as refs ( 48 ) and ( 49 )). …”

“… Solubility of Na 2 C 2 O 4 in aqueous solutions of NaNO 3 , NaCl, and NaOH (data from refs ( 48 ) and ( 49 )). …”

Editorial: Guidelines for the Measurement of Solid–Liquid Solubility Data at Atmospheric Pressure

“…Crystallization of a certain solid phase often needs to be initiated by seeding (although this method does not always promote precipitation of the same phase, as has been found, for example, in the case of magnesium sulfate hydrates). Alternatively, the temperature dependence of solubility can be exploited by changing T in such a direction that more of the equilibrated phase dissolves, followed by a return to the desired equilibration temperature …”

“…Various methods used in the older literature have been discussed by Zimmerman . While modern trace analytical techniques have enabled the measurement of very low solubilities, the uncertainties involved are much larger (also because of the presence, often in vast excess, of other solution components such as background electrolytes) than those in the case of higher solubilities, where the most reliable and accurate methods of quantitative analysis, gravimetry and volumetry, can be applied. , For moderately to highly soluble solutes, it would therefore be counterproductive to dilute saturated solutions by many orders of magnitude then use a routine trace-analytical method such as atomic absorption or inductively coupled plasma spectrometry. Characterization of the solid phase. After the solubility experiment has been finished and the phases have been separated, the mother liquor permeating the “wet residue” needs to be removed by washing the solid with a suitable solvent, filtering and drying (usually applicable to sparingly soluble solids).…”

“…Alternatively, the temperature dependence of solubility can be exploited by changing T in such a direction that more of the equilibrated phase dissolves, followed by a return to the desired equilibration temperature. 15 In any case, a heterogeneous system of solution + solid solute is produced that requires appropriate experimental protocols for steps (i) to (vii) listed above.…”