Volumes of ionization of dicarboxylic acids in aqueous solution from density measurements at 25°C

Abstract

The densities of aqueous solutions of the dicarboxylic acids [CH₂]_n(COOH)₂(n= 0 – 5) and their mono- and di-socium salts have been measured at 25°C and used to calculate their apparent molal volumes. These have been used to obtain volumes of ionization for both dissociation reactions. The volumes of ionization, except for the second dissociation reaction of malonic acid, lie within the limits –6.7 to –14.2 cm³ mol^–1. The upper limit, –6.7 cm³ mol^–1, seems to originate from the volume change accompanying the dissociating proton only, and the lower limit arises since the charge of the acid anion only affects the hydration sheaths of the nearest CH₂-groups.