Collect. Czech. Chem. Commun. 1991, 56, 1184-1192

Determination of limiting molar conductivities of weak organic acids in aqueous solutions

Begoña García*, Inmaculada Domingo, Pedro L. Domingo and José M. Leal

Departamento de Química Física, Universidad de Valladolid, Colegio Universitario Integrado, 09001 Burgos, Spain


Conductance, potentiometric, and spectrophotometric measurements have been made at 25°C of aqueous solution containing sulfanilic, hippuric, mandelic, and 3,5-dinitrosalicylic acids at different concentrations. Conductance data were analyzed using the methods of Fuoss-Kraus, Kraus-Parker, and Shedlovsky for conductivity of the free ions. Using the calculated limiting conductances, activity coefficients, and degrees of dissociation, the dissociation constants of the weak acids were determined. From plots Δ vs c1/2, reliable values for Δ0 were estimated, using a computer program, and by means of an iterative method the proper value of Δ0 was determined, independently of that initially introduced. Values of pK were also obtained from potentiometric and spectrophotometric measurements. Evidence for the existence of univalent and divalent ions in aqueous solutions of 3,5-dinitrosalicylic acid was obtained spectrophotometrically, this fact justifying the poorer results provided by conductance measurements.