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. 2. Estimation of Parameters for the Model for the First Dissociation Constant and Tests and Use of the Resulting Activity Coefficient Equations

Abstract

Previously (in Part 1, J. Chem. Eng. Data 2006, 51, 777−784), equations were determined for the calculation of the second stoichiometric (molality scale) dissociation constant (Km2) of phthalic acid in buffer solutions containing potassium hydrogen phthalate (KHPh), dipotassium phthalate, and potassium 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 were based on the single-ion activity coefficient equations of the Huckel type. The parameters of phthalate species for these equations and the second thermodynamic dissociation constant of this acid at various temperatures were determined from Harned cell data of Hamer and Acree (J. Res. Natl. Bur. Stand. 1945, 35, 381−416), and the resulting parameter values were also tested with these data. In the present study, the corresponding equations were determined fr...