Determination of Stoichiometric Dissociation Constant of Ammonium Ion in Aqueous Potassium Chloride Solutions at 298.15 K

Abstract

Equations were developed for the calculation of the stoichiometric (molality scale) dissociation constants, K m , of ammonium ion in aqueous KCl solutions at 298.15 K from the thermodynamic dissociation constant, K a , of this acid and the ionic strength, I m , of the solutions. Excess KCl was used in the solutions considered so that this salt in practice determined the ionic strength of these solutions. Equations for K m were based on the single-ion activity coefficient equations of the Hückel type. Potentiometric titration data measured with a glass electrode cell were used in the estimation of the parameters for the Hückel equations. By means of the calculation method suggested in this study, K m can be obtained almost within experimental error up to I m of 1.0 mol kg −1 for KCl solutions. The K m values obtained by this method were compared to the literature results obtained from the Harned cell data of Bates and Pinching (1949) and from the concentration cell data of Everett and Wynne-Jones (1938) measured with hydrogen electrodes on cells containing two liquid junctions.