Alternative formalism for the evaluation of the activity coefficients on ternary electrolyte solutions from osmotic coefficient data

CHIALVO, ABEL C.; PASSAMONTI, FRANCISCO J.; GENNERO DE CHIALVO, MARÍA R.

FLUID PHASE EQUILIBRIA

ELSEVIER SCIENCE BV

Año: 2021 vol. 547

0378-3812

An alternative method is presented, which is independent of any physicochemical model of the electrolyte solution, for the evaluation of the mean ionic activity coefficient in molal scale, γ±i (i: 2,3), of the solutes of a ternary solution (1?2?3), starting from experimental data of the osmotic coefficient on composition ϕexp(m,xi). It is based on the dependence of ln γ±i on ϕ originally derived by H.A.C. McKay and confirmed by S.G. Canagaratna and M. Maheswaran as a particular solution of Gibbs-Duhem equation for multicomponent systems. Its application involves the integration of both ϕ and its derivative ∂ϕ/∂mi, so that it requires a very precise correlation of the dependence ϕexp(m,xi). Therefore, in order to achieve the required precision, the theoretical expression ϕ(m,xi) is developed as the sum of three contributions, (i) ϕDH: the limiting behaviour given by the Debye-Hückel equation for multicomponent systems, (ii) ΔϕDDH: the sum of the deviations to the Debye-Hückel behaviour of the corresponding binary solutions (1?2 and 1?3) and (iii) ΔϕM: a contribution of mixing effect. Finally, introducing the resulting ϕ(m,xi) into the Gibbs-Duhem equation and operating, the corresponding expression of ln γ±i (m,xi) is derived. The capacity of the ϕ(m,xi) equation to correlate the dependence ϕexp(m,xi), the methodology employed to obtain the parameters values, as well as the ln γ±i (m,xi) resulting dependence are illustrated through its application to the analysis of two ternary systems.