Ionic Strength Dependence of Formation Constants. Part 7. Protonation Constants of Low Molecular Weight Carboxylic Acids at 10, 25 and 45 °C

The protonation of ten carboxylic acids (formic, propionic, malonic, succinic, phthalic, itaconic, malic, oxydiacetic, thiodiacetic and thiodipropionic) has been studied potentiometrically at 10 (except succinic acid), 25 and 45°C (except succinic, malonic and oxydiacetic acids) at eight ionic strengths, 0.04 ⩽ I ⩽ 0.8 mol 1−1, using tetraethylammonium iodide as background salt. As in previous works of this series, the dependence of protonation constants on ionic strength has been studied using the simple and general equation log β = f(I, z*, p*, c0, c1, d) (z* and p* are parameters depending on the stoichiometry of reactions under study; c0, c1 and d are general empirical parameters valid for all reactions). Furthermore, from the temperature coefficients of c0, c1 and d, the dependence of ΔH on ionic strength has been obtained. The results have been compared with previous findings.