Calculation of the first and second stoichiometric dissociation constants of glycine in aqueous sodium chloride solutions at 298.15 K

Abstract

AbstractEquations for the calculation of the first and second stoichiometric dissociation constants (Km,1 and Km,2) of glycine in aqueous NaCl solutions at 298.15 K were determined by a method developed recently. In this method, a simple equation of the Hückel type is used for single‐ion activity coefficients. The thermodynamic dissociation constants of this amino acid were taken from the literature, and the parameters for the activity coefficient equation were determined from the electromotive force data measured on cells without a liquid junction. These data were taken from the literature, and they were also used to test the resulting equations. The equations predict the data usually within ±0.3 mV. The recommended activity coefficients equations were also tested with literature results measured on cells containing a liquid junction. The activity coefficient equations apply in the best case up to ionic strengths of about 3 mol kg−1. For the glycine solutions where NaCl alone determines the ionic strength, the recommended Km,1 and Km,2 are tabulated at rounded ionic strengths. Possibilities to calculate the ionic activity coefficients for glycine species by means of the Pitzer equations are also considered.