Solubility of ammonia in pure aqueous and multicomponent solutions

The thermodynamic Henry's law constant (K_H/mol kg^-1 atm^-1) of the weak electrolyte NH₃ is described by the equation In (K_H) = -8.09694 + 3917.507/T - 0.00314T, from 273 to 313 K. Measured NH₃ solubilities in both pure aqueous and multicomponent solutions agree well with calculations using the Pitzer thermodynamic model to predict osmotic and activity coefficients. Partial pressure and heat of dilution data were used to determine the activity coefficient of NH₃ (γ_NH3). In pure aqueous solutions where dissociation is not significant this is given by γ_NH3 = exp(2m_NH3λ_NH3,NH3), where λ_NH3,NH3 = 0.033161 - 21.12816/T + 4665.1461/T² from 273 to 313 K. Ion-NH₃ interaction parameters were obtained by using partial pressure, salt solubility, and partitioning data for the following ions at 298.15 K: Li⁺, Na⁺, K⁺, NH₄⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, F^-, Cl^-, Br^-, I^-, OH^-, CNS^-, NO₃^-, NO₂^-, ClO₃^-, ClO₄^-, S^2-, SO₃^2-, CH₃COO^-, HCOO^- and (COO)₂^2-. Parameter values are found to be simply related to ion charge and size. © 1989 American Chemical Society.