On the Predictive Ability of the New Thermodynamics of Electrolyte Solutions

Abstract

This work highlights the main elements of the new thermodynamic approach to electrolyte solutions and demonstrates its ability to make predictions for mixed salt systems. After a review of the state of affairs before the measurement of activities of individual ions, experimental set-ups used for these measurements are described and the essential elements of different methods used to reduce the data are discussed. The results of experiments carried to test a possible bias introduced by uncertainty in the values of the junction potential are emphasized. It is purported that the thermodynamic treatment proposed by Lin and Lee is of general application and ensures the thermodynamic consistency of correlations previously proposed for the individual ionic activities. It is shown that the use of a more complex form for the contribution of long-range interactions to ionic activities leads to a simpler form of the osmotic coefficient. As an example of application, the predictions of the equilibrium pressure over NaCl + KCl, NaBr + KBr, and NaCl + CaCl 2 aqueous solutions, at different temperatures and compositions, are compared with independently measured experimental data.

Effect of the reference solution in the measurement of ion activity coefficients using cells with transference at T=298.15K

“…At this point, it seems safe to conclude that for most single electrolyte aqueous solutions of practical interest, the activity coefficients of individual ions are either known with reasonable accuracy or they are determinable by rather standard procedures. On the other hand, the work to evaluate ionic activities in mixtures is just starting to emerge [16] and the work of modelling the ionic activities in mixtures is in preliminary steps [17,18]. As there is still some discussion about the measurability of ionic activities [19,20], the additional experimental evidence presented here supports the idea that these properties are measurable [20].…”

On the measurement of the real values of individual ionic activities: A chemical engineering perspective

“…In fact, this analytical treatment of partial differentiation of an excess Gibbs energy function was used by Pitzer (1995) to obtain expressions for ionic activities from mean ionic activity data. As discussed elsewhere (Wilczek-Vera and Vera, 2009b) this typical way of handling data for non-electrolyte mixtures seems inappropriate for the treatment of electrolyte solutions. For the thermodynamic treatment of electrolyte solutions it seems better to use a model for the ionic activities and an equation proposed by Lin and Lee (2003) for the calculation of the activity of water.…”

Chapter 27 The Activity of Individual Ions Measuring and Modeling

“…The measurability of the activity of individual ions may not be considered to be definitely settled, as there are people who still maintain that these measurements are impossible to achieve in concentrated solutions above 0.01 m. A historical perspective of roots of that point of view is given elsewhere [1] and discussed briefly in the closing comments of this chapter. The arguments in favor of the measurability of the activity of individual ions have been presented elsewhere [1,2,6,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. In both cases, the editor of the respective journal closed the debate once the informed reader could judge how much each of the two sides knew about the subject.…”

“…Lin and Lee [40], in an impressively insightful derivation, elegantly solved this problem. Further study using the Lin and Lee equation [26] showed that a particularly simple expression for the osmotic coefficient is obtained with a minor modification of Equation 27. Lin and Lee considered the ionic composition of the multi-ion aqueous solution to be known by an independent chemical analysis.…”

“…Lin and Lee considered the ionic composition of the multi-ion aqueous solution to be known by an independent chemical analysis. The expression for the osmotic coefficient obtained using Equation 27.43 and the Lin and Lee equation is Figure 27.3 presents the results of the prediction of the equilibrium pressure over aqueous solutions of mixed electrolytes with a common ion in comparison with experimental data available in the literature [26]. In all this process, the composition of [2].…”