Determination of Stoichiometric Dissociation Constants of Glycolic Acid in Dilute Aqueous Sodium or Potassium Chloride Solutions at 298.15 K

Abstract

Equations were determined for the calculation of the stoichiometric (molality scale) dissociation constant, K m , of glycolic acid in dilute aqueous NaCl and KCl solutions at 298.15 K from the thermodynamic dissociation constant, K a , of this acid and from the ionic strength, I m , of the solution. The salt alone determines mostly the ionic strength of the solutions considered in this study, and the equations for K m were based on the single-ion activity coefficient equations of the Hückel type. The data measured by potentiometric titrations in a glass electrode cell and the literature data obtained by Harned cells were used in the estimation of the parameters for the Hückel equations of glycolate ions. By means of the calculation method based on the Hückel equations, K m can be obtained almost within experimental error at least up to I m of about 0.5 mol kg −1 for glycolic acid in NaCl and KCl solutions.