Determination of stoichiometric dissociation constants for propionic acid in aqueous sodium or potassium chloride solutions at 298.15 K

摘要

Single-ion activity coefficient equations were determined for the calculation of the molality scale dissociation constants, K-m, for propionic acid in dilute 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 Huckel type, and K, 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, values from the titration data were considered. The activity parameters for the Huckel equation were determined from the K, values calculated by all of these methods. The parameters obtained by the different methods are very consistent with each other and also with the Huckel parameters obtained previously for light fatty acids from the literature data measured by 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 Huckel equations, K,can be obtained by this method almost within experimental error for propionic acid in NaCl and KCI solutions up to I-m of about 1 mol kg(-1). [References: 22]