ИСТИНА

The extended Debye-Hückel theory [1] which allows for concentration variation of electrolyte solution static permittivity is employed to predict activity coefficients in aqueous solutions of sodium salts with various univalent anions (NaCl, NaBr, NaI, NaNO3, NaClO4 and NaSCN) at ambient conditions. Calculations without parameter fitting reproduced the activity coefficients for NaI in the concentration range up to 6 mol/kg and for NaSCN up to 2 mol/kg. In case of other solutions calculations underestimate water activity coefficient at concentrations beyond 0.5 mol/kg. The model was extended to include ion pairing to gain better agreement between calculated activity coefficients and experimental data. The ion pairing equilibrium constants were estimated and compared with available literature values. The extent of ion pairing was found to increase in the sequence NaI < NaSCN < NaBr < NaCl < NaClO4 < NaNO3 with violation of the Collins rule [2] in case of polyatomic oxygen-containing anions. Financial support by RFBR (grant N 16-03-00725) is gratefully acknowledged. 1. I.Yu. Shilov, A.K. Lyashchenko. J. Phys. Chem. B, 2015, 119, 10087. 2. K.D. Collins. Methods, 2004, 34, 300-311.