Electromotive force studies of electrolytic dissociation. Part 13—Dissociation constants of some dicarboxylic acids at zero ionic strength in water and 10 % ethanol

Abstract

pK₁ and pK₂ values at zero ionic strength of some dicarboxylic acids in water and in 10 % ethanol (by volume) at 25 and 40°C have been compiled from e.m.f. measurements of a glass electrode, HCl, buffer, AgCl cell. As in previous work (Part 12) dilute HCl was used to calibrate the cell and the pKs assessed after additions of stock buffer solution. Critical comparisons with published figures for malonic and succinic acids in water, obtained from measurements with the classical Harned cell H₂, Pt, buffer, NaCl, AgCl show that the glass electrode cell can yield answers of similar precision. Provided data are obtained down to an ionic strength ≈ 0.01, pK₂ values show little dependence (≈ 1 %) on reasonable estimates of the parameters used in the Debye–Huckel activity coefficient expression. It is suggested that published K₂ values for succinic acid in water that were derived from the Harned cell are ≈ 2 % too high.