Thermodynamics of aqueous EDTA systems: Apparent and partial molar heat capacities and volumes of aqueous EDTA⁴⁻, HEDTA³⁻, H₂EDTA²⁻, NaEDTA³⁻, and KEDTA³⁻ at 25 °C. Relaxation effects in mixed aqueous electrolyte solutions and calculations of temperature dependent equilibrium constants

Abstract

Calorimetric and densimetric measurements have led to apparent molar heat capacities and volumes for aqueous solutions of the mixed electrolytes [(CH3)4N]4EDTA + (CH3)4NOH, Na4EDTA + NaOH, and K4EDTA + KOH, and single electrolytes Na2H2EDTA and [(CH3)4N]3[HEDTA] at 25 °C. We have analyzed these results in terms of Young's rule and Pitzer's ion interaction model to obtain standard state partial molar heat capacities and volumes of EDTA4−(aq), HEDTA3−(aq), H2EDTA2−(aq), NaEDTA3−(aq), and KEDTA3−(aq) at 25 °C. For these calculations it was also necessary to evaluate the "relaxation" contribution to the measured heat capacities of some solutions. The partial molar heat capacities obtained here have been used with enthalpies from previous investigations for calculations of several equilibrium constants over wide ranges of temperature; volumes can be used for similar calculations of the effects of pressure.

Apparent and partial molar heat capacities and volumes of aqueous adipic acid, l-tartaric acid, and their sodium salts atT= 298.15 K

“…In recent years, Apelblat and Manzurola (20,21) determined the apparent molar volumes of several organic acids and their salts at T = 298.15 K over a wide molality range. The experimental values for tartaric acid from our work agree with Apelblat and Manzurola's result to within 0.5 cm 3 · mol −1 over the molality range of our experiments, but the extrapolated value of V o φ based on equation (19) differs from (21) 115.67(0.14) 115.66 (7) 115.97 (20) 115.15 (21) NaHA ( (7) 83.4 (21) 82.23 (22) NaHT ( to within 1 cm 3 · mol −1 above m = 0.1 mol · kg −1 , but the difference in V o φ (Na 2 T, aq) is 1.0 cm 3 · mol −1 . The discrepancies apparently arise because no corrections for the dissociation of the acid and its salts were considered in Apelblat and Manzurola's study.…”

“…For C o p,φ , the difference is less than 5 J · K −1 · mol −1 , and for V o φ , the difference is within 0.6 cm 3 · mol −1 . (8) The standard partial molar heat capacity and volume changes corresponding to the stepwise ionization of adipic acid and tartaric acid are listed in table 5.…”

Experimental Support for a Desolvation Energy Term in Governing Equations for Binding Equilibria

“…Under this buffer condition, changes in the initial and final pH values were found to be negligible for the contents of the sample cell in trials using the most concentrated EDTA solution (12.5 mM). At pH 6.2, EDTA exists in approximately equal proportions of the mono- and di-protonated species, 10 and the binding affinity should fall below the upper limit for practical measurements by ITC. 11 …”

Morphology of barium sulfate synthesized with barium(II)–aminocarboxylate chelating precursors

“…The standard Gibbs free energy change for the Ba II ±EDTA complex was calculated from eqn. (9), in which the molar heat capacity was approximated as being constant 29,30 without temperature dependency.…”