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

Abstract

Apparent molar heat capacities and volumes have been determined for aqueous solutions of tartaric acid (H 2Tar, Tar=C 4H 4O 6), two buffer solutions of (H 2Tar/NaHTar) and (NaHTar/Na 2Tar), and solutions of disodium tartrate (Na 2Tar) at four temperatures in the range 283.15⩽ T/K⩽328.15 at p=1 MPa. Apparent molar volumes for H 2Tar(aq) and Na 2Tar(aq) have been measured at temperatures 377.15⩽ T/K⩽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 ∘ and volumes V ∘ for the species H 2Tar(aq), HTar −(aq) and Tar 2−(aq) over the range of experimental measurements. The temperature dependence of V ∘ for Na 2Tar(aq) is consistent with other aqueous electrolytes, while that of H 2Tar(aq) may be anomalous, in that it does not show divergence towards increasingly positive values with increasing temperature.