Determination of the second stoichiometric dissociation constants of glycine in aqueous sodium or potassium chloride solutions at 298.15 K

Abstract

Equations were determined for the calculation of the second stoichiometric (molality scale) dissociation constant, Km2, of glycine, in aqueous NaCl and KCl solutions at 298.15 K, from the thermodynamic dissociation constant, Ka2, of this acid and the ionic strength, Im, of the solution. The ionic strength of the solutions considered in this study is determined mostly by the salt alone, and the equations for Km2 were based on the single-ion activity coefficient equations of the Hückel type. New data measured by potentiometric titrations in a glass electrode cell were used in the estimation of the parameters for the Hückel equations of glycine species. By means of the calculation method suggested in this study, Km2 can be obtained almost within experimental error up to an Im of about 1.0 mol kg–1 for glycine in NaCl and KCl solutions. The Km2 values obtained by these methods were also compared with the values suggested in the literature for this quantity.Key words: ionic strength dependence, stoichiometric dissociation constant, Debye–Hückel equation, potentiometry, glycine.