Re-evaluation of the First and Second Stoichiometric Dissociation Constants of Phthalic Acid at Temperatures from (0 to 60) °C in Aqueous Phthalate Buffer Solutions with or without Potassium Chloride. 1. Estimation of the Parameters for the Hückel Model Activity Coefficient Equations for Calculation of the Second Dissociation Constant

Abstract

Equations were developed for the calculation of the second stoichiometric (molality scale) dissociation constant (Km2) of phthalic acid in buffer solutions containing potassium dihydrogen phthalate, hydrogen phthalate, and chloride from the determined thermodynamic values of this dissociation constant (Ka2) and the molalities of the components in the solutions. These equations apply at temperatures from (0 to 60) °C up to ionic strengths of about 0.5 mol·kg-1, and they are based on the single-ion activity coefficient equations of the Huckel type. The parameters of phthalate ions for these equations and the thermodynamic values of the second dissociation constant of this acid at various temperatures were determined from the Harned cell data measured by Hamer and Acree (J. Res. Natl. Bur. Stand. 1945, 35, 381−416). In these parameter estimations, the stoichiometric values of the first dissociation constant of phthalic acid were needed, and these values were obtained from the Harned cell results of Hamer et ...