ИСТИНА

Activity coefficients in aqueous solutions of alkali metal nitrates at 298 K are analyzed and modeled in the framework of the extended Debye-Hückel theory (EDH) [1] using the experimental solution static permittivity data [2]. Without parameter fitting, the theory reproduces the order of activity coefficients in the solutions of salts with different cations as shown in the figures. This order is explained by decreasing hydration of cations with increasing cation radius and also by increasing ion paring in solutions in the same series which is evidenced by conductivity measurements [3]. The leveling of activity coefficients in solutions of potassium, rubidium and cesium ions in the presence of nitrate ion is also reproduced by the model taking into account the close values of solution permittivities and cation radii. The work was supported by the Russian Foundation for Basic Research (project number 19-03-00033) and by IGIС RAS state assignment. 1. I.Yu. Shilov, A.K. Lyashchenko. J. Phys. Chem. B., 2015, 119, 10087-10095. 2. J. Barthel, F. Schmithals, H. Behret. Z. Phys. Chem. N. F., 1970, 71, 115-131. 3. M.-C. Justice, R. Bury, J.-C. Justice. Electrochim. Acta, 1971, 16, 687-700.