Abstract
A Picker flow microcalorimeter and a flow densimeter were used to obtain apparent molar heat capacities and apparent molar volumes of aqueous solutions of Na3PO4 and mixtures of Na2HPO4 and NaH2PO4. Identical measurements were also made on solutions of tetramethylammonium salts to evaluate the importance of anion-cation interaction. The experimental apparent molar properties were analyzed in terms of a simple extended Debye-Hückel model and the Pitzer ion-interaction model, both with a suitable treatment for the effect of chemical relaxation on heat capacities, to derive the partial molar properties of H2PO −4 (aq), HPO 2−4 (aq) and PO 3−4 (aq) at infinite dilution. The volume and heat capacity changes for the second and third ionization of H3PO4(aq) have been determined from the experimental data. The importance of ionic complexation with sodium is discussed.
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Bianchi, H., Tremaine, P.R. Thermodynamics of aqueous phosphate solutions: Apparent molar heat capacities and volumes of the sodium and tetramethylammonium salts at 25°C. J Solution Chem 24, 439–463 (1995). https://doi.org/10.1007/BF01004477
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DOI: https://doi.org/10.1007/BF01004477