Apparent and standard partial molar heat capacities and volumes of aqueous tartaric acid and its sodium salts at elevated temperature and pressure

Apparent molar heat capacities and volumes have been determined for aqueous solutions of tartaric acid (H(2)Tar, Tar = C4H4O6), two buffer solutions of (H(2)Tar/NaHTar) and (NaHTar/Na(2)Tar), and solutions of disodium tartrate (Na(2)Tar) at four temperatures in the range 283.15 less than or equal to T/K less than or equal to 328.15 at p = 1 MPa. Apparent molar volumes for H(2)Tar(aq) and Na(2)Tar(aq) have been measured at temperatures 377.15 less than or equal to T/K less than or equal to 529.15 and p = 10.4 MPa. The experimental results have been represented with a model to describe the molality and temperature dependence. Extrapolations to infinite dilution yielded standard partial molar heat capacities C(p)degrees and volumes Vdegrees for the species H(2)Tar(aq), HTar(-)(aq) and Tar(2-)(aq) over the range of experimental measurements. The temperature dependence of Vdegrees for Na(2)Tar(aq) is consistent with other aqueous electrolytes, while that of H(2)Tar(aq) may be anomalous, in that it does not show divergence towards increasingly positive values with increasing temperature. (C) 2004 Elsevier Ltd. All rights reserved.