Partial molal volumes and volumes of ionization of hydroxycarboxylic acids in aqueous solution at 25, 30 and 35°C

Abstract

The densities of aqueous solutions of the homologous series of α-hydroxycarboxylic acids up to α-hydroxyhexanoic acid and their sodium salts and tartaric acid and its mono- and di-sodium salts have been measured at 25, 30 and 35°C.

The molar conductances of aqueous solutions of the same α-hydroxycarboxylic acids and those of β- and γ-hydroxybutyric acid and their sodium salts have been measured in the pressure range 1–1200 bar at 25, 30 and 35°C.

Volumes of ionization calculated both from density and conductance measurements are in good agreement, and show a minimum value of – 13.8 ± 0.2 cm³ mol^–1 for the higher homologues. Partial molal volumes have been calculated, and used to determine the partial molal volume of the hydroxymethylene group. The additivity of group partial molal volumes is confirmed.