DETERMINATION OF THE HYDROGEN-ION AND CHLORIDE-ION ACTIVITIES IN HYDROCHLORIC-ACID

A potentiometric method has been used for the determination of the values of hydrogen ion and chloride ion activities (αH and αCl respectively) in solutions of hydrochloric ranging in concentration from 1 to 9 M. The potentials of the couples H2(g)/H+ and Cl-/Cl2(g) where measured at zero current with respect to the standard potentials of ferrocene and tetracene which are supposed to be independent of solvent. The values of αH and αCl were obtained from the Nernst equation. A comparison is made with literature data including the values of ionic activities calculated from the expressions of Bates et al. These expressions require the individual activity coefficients of the ions in concentrated solutions of unassociated uni-univalent chloride electrolytes based on the Stokes-Robinson hydration theory. The variations of αH and αCl with the concentration of hydrochloric solution were used for the exploitation of experimental results. For example, the equilibrium constant of formation of the complex AgCl43- which prevails in concentrated hydrochloric acid has been determined from the variation of the redox potential of the Ag+/Ag system with log αCl. © 1990.