Re-evaluation of the Second Stoichiometric Dissociation Constants of Phosphoric Acid at Temperatures from (0 to 60) °C in Aqueous Buffer Solutions with or without NaCl or KCl. 1. Estimation of the Parameters for the Hückel Model Activity Coefficient Equations

Abstract

Equations were determined for the calculation of the second stoichiometric (molality scale) dissociation constant (Km2) of phosphoric acid in buffer solutions containing sodium dihydrogen phosphate, sodium hydrogen phosphate, and sodium chloride and the corresponding systems where mixed potassium and sodium salts were used from the determined thermodynamic values of this dissociation constant (Ka2) and the molalities of the components in the solutions. These equations were based on the single-ion activity coefficient equations of the Huckel type. The parameters of the phosphate 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 of Bates and Acree (1943 and 1945), and these data extend at temperatures from (0 to 60) °C up to ionic strengths of about 0.5 mol kg-1. All calculations from these data were completely revised, and all parameters estimated seem to depend in a simple way on the temp...