Home – Home – Jornals – Journal of Structural Chemistry 2014 number 3

The apparent volumes of the salts in the systems H₂O - NH₄Cl (298 K) and H₂O - NH₄NO₃ (273, 298, and 323 K) are reproduced with an accuracy of 0.03-0.01 cm ³/mol by the equation φ = φ⁰ + Aw₂^0,5 + Вw₂, where w₂ is the salt content (mass fractions). The study shows that there is a correspondence between the critical (for determining the hydration number) structural parameters-the intrinsic volume of the electrolyte and the volume of water in ion hydration shells-and the limiting (at w₂ = 1) partial molar volumes of the components. The hydration numbers at infinite dilution are 6.9 for NH₄Cl at 298 K and 9.1, 6.7, and 6.4 for NH₄NO₃ at 273, 298, and 323 K. The water volume in ion hydration shells decreases in the sequence: NO₃^¯ Cl^-, and NH₄⁺ The hydration numbers decrease with increasing salt concentration. The study shows that within a simpler model φ = φ⁰ + aw₂^0,5, the hydration numbers are temperature independent.