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

Abstract

Equations were determined for the calculation of the stoichiometric (molality scale) dissociation constant Km of formic acid in dilute aqueous NaCl and KCl solutions at 298.15 K from the thermodynamic dissociation constant Ka of this acid and from the ionic strength Im of the solution. The salt alone determines mostly the ionic strength of the solutions considered in this study, and the equations for Km were based on the single-ion activity coefficient equations of the Hückel type. The data measured by potentiometric titrations in a glass electrode cell were used in the estimation of the parameters for the Hückel equations of formate ions. The Hückel parameters obtained in these estimations agree well with those published previously for acetate ions, and therefore, the acetate parameters are also recommended for formate ions. By means of the calculation method based on the Hückel equations, Km can be obtained almost within experimental error at least up to Im of about 2 mol kg-1 for formic acid in NaCl and KCl solutions.