Comparison of different methods for calculation of the stoichiometric dissociation constant of acetic acid from results of potentiometric titrations at 298.15 K in aqueous sodium or potassium chloride solutions

Abstract

Single-ion activity coefficient equations were determined for the calculation of the molality-scale dissociation constants, K m, for acetic acid in aqueous NaCl or KCl solutions at 298.15 K. The salt alone determines the ionic strength, I m, of the solutions considered in this study. The activity coefficient equations are of the Hückel type, and K m can be calculated by those for a certain ionic strength from the thermodynamic dissociation constant. The data used for the estimation of the parameters for these equations were measured by potentiometric titrations in a glass electrode cell. Three different methods to calculate the experimental K m values from the titration data were considered. The activity parameters for the Hückel equation were determined from the K m values calculated by all of these methods. The parameters obtained by these methods are very consistent with each other and also with the Hückel parameters obtained previously for acetic acid from the literature data measured on Harned cells. The final activity parameters recommended in this study seem to be reliable. Despite the theoretical difficulties associated with the single-ion activity coefficients and the simplicity of the calculation method based on Hückel equations, K m can be obtained by this method almost within experimental error for acetic acid in NaCl and KCl solutions up to I m of about 1 mol kg −1. It was shown in this study, in addition, that the K m values obtained by the Hückel equations agree well also with those calculated by the Pitzer equations.