Thermodynamics of Aqueous Diethylenetriaminepentaacetic Acid (DTPA) Systmes: Apparent and Partial Molar Heat Capacities and Volumes of Aqueous H_2DTPA~(3-), DTPA~(5-), CuDTPA~(3-), and Cu_2DTPA~- from 10 to 55 deg C

摘要

Apparent molar heat capacities and volumes have been determined for aqueous solutions of the mixed electrolytes Na_5DTPA + NaOH, Na_3CuDTPA + NaOH, and NaCu_2DTPA + NaOH, and the single electrolyte Na_3H_2DTPA (DTPA= diethylenetriaminepentaacetic acid) at temperatures from 10 to 55 deg C. The experimental results have been analyzed in terms of Young's rule with the Guggnheim form of the extended Debye-Huckel equation and the Pitzer ion-interaction model. These calculations led to standard partial molar heat capacities and volumes for the species H_2DTPA~(3-)(aq), DTPA~(5-)(aq), CuDTPA~(3-)(aq), and Cu_2DTPA~-(aq) at each temperature. The partial molar properties at 0.1 m ionic strength were also calculated. The standard partial molar properties were extrapolated to elevated temperatures with the revised Helgeson-Kirkham-Flowers (HKF) model. Values for the partial molar heat capacities from the HKF model have been combined with the literature data to estimate the ionization constants of H_2DTPA~(3-)(aq) and the formation constant of the CuDTPA~(3-)(aq) copper complex at temperatures up to 300 deg C.