Ionic solutes binary systems

Bhujrajh P, Deenadayalu N. Liquid densities and excess molar volumes for binary systems (ionic liquids plus methanol or water) at 298.15, 303.15 and 313.15K, and at atmospheric pressure. J. Solut. Chem. 2007. 36, 631-642. 

Two activity coefficient models have been developed for vapor-liquid equilibrium of electrolyte systems. The first model is an extension of the Pitzer equation and is applicable to aqueous electrolyte systems containing any number of molecular and ionic solutes. The validity of the model has been shown by data correlation studies on three aqueous electrolyte systems of industrial interest. The second model is based on the local composition concept and is designed to be applicable to all kinds of electrolyte systems. Preliminary data correlation results on many binary and ternary electrolyte systems suggest the validity of the local composition model. 

While the early work on molten NH4CI gave only some qualitative hints that the effective critical behavior of ionic fluids may be different from that of nonionic fluids, the possibility of apparent mean-field behavior has been substantiated in precise studies of two- and multicomponent ionic fluids. Crossover to mean-field criticality far away from Tc seems now well-established for several systems. Examples are liquid-liquid demixings in binary systems such as Bu4NPic + alcohols and Na + NH3, liquid-liquid demixings in ternary systems of the type salt + water + organic solvent, and liquid-vapor transitions in aqueous solutions of NaCl. On the other hand, Pitzer s conjecture that the asymptotic behavior itself might be mean-field-like has not been confirmed. 

Graf D. L., Anderson D. E., and Woodhouse J. E. (1983) Ionic diffusion in naturally-occurring aqueous solutions transition-state models that use either empirical expressions or statistically-derived relationships to predict mutual diffusion coefficients in the concentrated-solution regions of 8 binary systems. Geochim. Cosmochim. Acta 47, 1985—1998. 

Iglesias-Otero M A, Troncoso J, Carballo E, et al. Density and refractive index for binary systems of the ionic liquid [bmimilBEJ with methanol, 1,3-dichloropropane, and dimethyl carbonate. J. Solut. Chem. 2007. 36, 1219-1230. 

In this study we restrict our consideration by a class of ionic liquids that can be properly described based on the classical multicomponent models of charged and neutral particles. The simplest nontrivial example is a binary mixture of positive and negative particles disposed in a medium with dielectric constant e that is widely used for the description of molten salts [4-6], More complicated cases can be related to ionic solutions being neutral multicomponent systems formed by a solute of positive and negative ions immersed in a neutral solvent. This kind of systems widely varies in complexity [7], ranging from electrolyte solutions where cations and anions have a comparable size and charge, to highly asymmetric macromolecular ionic liquids in which macroions (polymers, micelles, proteins, etc) and microscopic counterions coexist. Thus, the importance of this system in many theoretical and applied fields is out of any doubt. 

Table 23 provides an example where the two steps, HB and PT, have been treated on the same binary system in an apolar solvent where the solute-solvent interactions are minimized. Owing to the large negative AH values, even small decreases of a few tens of a degree shift the HB step to completion and increase notably the extent of PT. The larger negative entropy and the smaller negative enthalpy in the PT compared to the HB are both unfavorable to the ionic form, so that the PT equilibrium constants are smaller than the HB equilibrium constants for identical systems. 

Often i( is desirable 10 use equivalent ionic fractions to represent concentrations in the solution and resin phases. Thus, in a binary system,... 

These two models present a fascinating contrast in their approach to a complex problem. Pitzer stands back, as it were, from the details of ionic interactions, and builds up an empirical model of complex solutions from data on the simpler binary systems of whieh it is composed. No data as to individual ionic processes are required... 

As in the binary system, 0, =Xj, but for the ionic solutes 0, =2x] and 02=2xj. In Eq. (3.32) the factor 2 can be omitted when the molar area of the ions toi is introduced instead of (B. After consideration of the surface-to-bulk distribution of both electroneutral combinations of ions, we arrive at the equation for the adsorption isotherm of the two surfactants RiX and R2X, respectively... 

In the phenomenological model of Kahlweit et al. [46], the behavior of a ternary oil-water-surfactant system can be described in terms of the miscibility gaps of the oil-surfactant and water-surfactant binary subsystems. Their locations are indicated by the upper critical solution temperature (UCST), of the oil-surfactant binary systems and the critical solution temperature of the water-surfactant binary systems. Nonionic surfactants in water normally have a lower critical solution temperature (LCST), Tp, for the temperature ranges encountered in surfactant phase studies. Ionic surfactants, on the other hand, have a UCST, T. Kahlweit and coworkers have shown that techniques for altering surfactant phase behavior can be described in terms of their ability to change the miscibility gaps. One may note an analogy between this analysis and the Winsor analysis in that both involve a comparison of oil - surfactant and water-surfactant interactions. 

The equilibrium = f(c ) or the partition between an ionic component in the solid or resin phase and in the fluid phase of multicomponent systems depends on many material properties and the temperature and has to be measured. Things are easier for binary systems in which the ionic species a is exchanged. With the concentration q and the mass fraction in the solid or resin phase and the concentration C3 and the mass fraction in the liquid or solution phase the equilibrium =/(Ca) or a = f (y ) cau be described by the mass actiou equilibriiun Constant or selectivity coefficient (see (9.3-3)) ... 

The two-term crossover Landau model has been successfully applied to the description of the near-critical thermodynamic properties of various systems, that are physically very different the 3-dimensional lattice gas (Ising model) [25], one-component fluids near the vapor-liquid critical point [3, 20], binary liquid mixtures near the consolute point [20, 26], aqueous and nonaqueous ionic solutions [20, 27, 28], and polymer solutions [24]. 

Calculations involving diffusion processes in inhomogeneous multicomponent ionic systems have been recently performed by Kirkaldy [30] and Cooper [38]. They worked with the same assumptions that have been made in this section in which quasi-binary systems have been discussed constant molar volume of the solid solution, and independent fluxes of ions, which are coupled only by the electrical diffusion potential. The latter can be eliminated by the condition zJi 0 which means that local electroneutrality prevails. With these assumptions, and with a knowledge of the thermodynamics of the multicomponent system (which is a knowledge of the activity of the electroneutral components as a function of composition), the individual ionic fluxes can be calculated explicitly with the help of the ionic mobilities and the activity coefficients of the components. 

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