Individual Activity Coefficients of Ionic Species.

Abstract : Research investigations on an attempt to measure the absolute magnitude of activity coefficients of individual ionic species have been continued. In support of this objective, experimental measurements were made of the non-isothermal temperature coefficient of the Ag/AgCl/Cl(-) electrode in the presence of KCl and HCl as electrolytes at mean temperature of 35.0C. It was found that a temperature difference much greater than 10 degrees can not be used to obtain the true temperature coefficient of the specified electrode. Experimental work was also carried out in order to prepare Pt--H2/H(+) electrodes having a small (10 to 20 microvolts) and constant asymmetry electric tension. Constant measurements of the expected magnitude were not obtained until a complicated system was developed for removing all traces of oxygen from the system. Experiments were begun on evaluating the influence of the Soret-effect on non isothermal electrode measurements. A system using both the interferometric and the potentionmetric techniques was designed. Additional testing and design changes are needed to reduce uncertainties in the results due to instabilities of hydrodynamic origin. A preliminary computation of the activity coefficient of the chloride ion using experimental results from this study yielded a value that was of the same order of magnitude as the theoretical values calculated by the Keilland and the Debye-Huckel theoretical equations. (Author)