Thermodynamics of aqueous diethylenetriaminepentaacetic acid (DTPA) systems: Apparent and partial molar heat capacities and volumes of aqueous H(2)DTPA(3-), DTPA(5-), CuDTPA(3-), and Cu(2)DTPA(-) from 10 to 55 degrees C

Apparent molar heat capacities and volumes have been determined for aqueous solutions of the mixed electrolytes Na(5)DTPA + NaOH, Na(3)CuDTPA + NaOH, and NaCu(2)DTPA + NaOH, and the single electrolyte Na(3)H(2)DTPA (DTPA = di ethylenetriaminepentaacetic acid) at temperatures from 10 to 55 degrees C. The experimental results have been analyzed in terms of Young's rule with t he Guggenheim form of the extended Debye-Huckel equation and the Pitzer ion -interaction model. These calculations led to standard partial molar heat c apacities and volumes for the species H(2)DTPA(3-)(aq), DTPA(5-)(aq), CuDTP A(3-)(aq), and Cu(2)DTPA(-)(aq) at each temperature. The partial molar prop erties at 0.1 m ionic strength were also calculated. The standard partial m olar properties were extrapolated to elevated temperatures with the revised Helgeson-Kirkham-Flowers (HKF) model. Values for the partial molar heat ca pacities from the HKF model have been combined with the literature data to estimate the ionization constants of H(2)DTPA(3-)(aq) and the formation con stant of the CuDTPA3-(aq) copper complex at temperatures up to 300 degrees C.