Electrolyte solutions properties

Solutions are usually classified as nonelectrolyte or electrolyte depending upon whether one or more of the components dissociates in the mixture. The two types of solutions are often treated differently. In electrolyte solutions properties like the activity coefficients and the osmotic coefficients are emphasized, with the dilute solution standard state chosen for the solute.c With nonelectrolyte solutions we often choose a Raoult s law standard state for both components, and we are more interested in the changes in the thermodynamic properties with mixing, AmjxZ. In this chapter, we will restrict our discussion to nonelectrolyte mixtures and use the change AmjxZ to help us understand the nature of the interactions that are occurring in the mixture. In the next chapter, we will describe the properties of electrolyte solutions. 

Despite this drawback there is an interest in science and technology in single-ion quantities for rationalizing the discussion of electrolyte solution properties. Various methods have been developed for their estimation based on extrathermodynamic assumptions, such as the following (1) The contributions of cation and anion are set equal for a salt composed of ions of equal charge and approximately equal radii (2) the results of measurements on a series of homologous electrolytes are extrapolated with regard to ionic radii or ionic volumes to zero ion size or zero reciprocal radii (3) the differences in conventional ionic properties are used for theoretically rationalized extrapolations and (4) the properties of ions are compared with those of isoelectronic neutral molecules of similar chemical constitution and size. 

Critically revised data of various electrolyte solution properties help scientists and engineers to overcome the time-consuming procedure of searching for reliable data for technical applications. Special knowledge-based databases undertake the interpolation, estimation, or simulation of data by theory-founded procedures differing fundamentally from those for nonelectrolytes. The reason for the difference is the essentially different reference states of electrolyte solutions which are the infinitely dilute solutions with at least three interacting components, namely solvent molecules, cations, and anions. In contrast, databases for nonelectrolytes always use the pure substances as the references. 

This handbook contains extensive tables of data for the more common Inorganic and organic aqueous electrolyte solutions. Properties covered include dielectric constants, activity coefficients, relative partial molar enthalpies, equilibrium constants, solubility products, conductivities, electrochemical potentials, Gibbs energies and enthalpies of formation, entropies, heat capacities, viscosities, and diffusion coefficients. Unfortunately, only a few of the tables contain references to the sources of the data. 

This very extensive (99 pages) chapter (no. 2 in Volume II) contains a general discussion of the effects of temperature and pressure on activity coefficients for both binary and mixed electrolyte solutions. Properties of interest are the partial molar volume, expansibility, compressibility, heat capacity, and enthalpy. There is also an excellent discussion of methods of estimating partial molar properties in mixed electrolyte solutions. There are 226 references to the literature. Tables of data are presented for Debye-HUckel limiting law slopes for the afJ parent molar volume, enthalpy, heat capacity, expansibility, and compressibility as a function of temperature parameters for the partial molar volumes of 30 aqueous electrolyes at 25 °C parameters for the partial molar expansibility of ten electrolytes at 25 C parameters for the partial molar compressibilities of 33 electrolytes at 25 °C values of the activity coefficients of aqueous NaCl solutions at 25 C as a function of pressure (up to 1000 bars) parameters for the partial molar enthalpies of 59 electrolytes at 25 C parameters for the partial molar heat capacities of 140 electrolytes at 25 °C and tables giving compositions and the partial molar properties of average seawater. 

Barthel J, Popp H (1992) Methods of the knowledge based system ELDAR for the simulation of electrolyte solution properties. Anal Chim Acta 265 259 266... 

This chapter discusses the electrolytic-solution properties of low-di-electric-constant nematic solvents. Dissolved substances, if electrolytes, can contribute only a fraction of their ions to the conductance because of equilibrium between the free ions and ion pairs. If the solute forms ions through intermediate charge-transfer reactions, additional equilibria must be considered. For nematics, the solvent fluidity is anisotropic, and the conductance depends on the direction of current flow with respect to the orientation of the fluid. The variation of the conductance with temperature is directly related to the variation with temperature of both the ionic equilibrium and the fluidity. 

Fig. XIII-10. Properties of colloidal electrolyte solutions—sodium dodecyl sulfate. (From Ref. 102a.)...

Rasaiah J C 1987 Theories of electrolyte solutions The Liquid State and its Electrical Properties (NATO Advanced Science Institute Series Vol 193) ed E E Kunhardt, L G Christophous and L H Luessen (New York Plenum)... 

Niobic Acid. Niobic acid, Nb20 XH2O, includes all hydrated forms of niobium pentoxide, where the degree of hydration depends on the method of preparation, age, etc. It is a white insoluble precipitate formed by acid hydrolysis of niobates that are prepared by alkaH pyrosulfate, carbonate, or hydroxide fusion base hydrolysis of niobium fluoride solutions or aqueous hydrolysis of chlorides or bromides. When it is formed in the presence of tannin, a volurninous red complex forms. Freshly precipitated niobic acid usually is coUoidal and is peptized by water washing, thus it is difficult to free from traces of electrolyte. Its properties vary with age and reactivity is noticeably diminished on standing for even a few days. It is soluble in concentrated hydrochloric and sulfuric acids but is reprecipitated on dilution and boiling and can be complexed when it is freshly made with oxaHc or tartaric acid. It is soluble in hydrofluoric acid of any concentration. 

Although ED is more complex than other membrane separation processes, the characteristic performance of a cell is, in principle, possible to calculate from a knowledge of ED cell geometry and the electrochemical properties of the membranes and the electrolyte solution. 

It is of special interest for many applications to consider adsorption of fiuids in matrices in the framework of models which include electrostatic forces. These systems are relevant, for example, to colloidal chemistry. On the other hand, electrodes made of specially treated carbon particles and impregnated by electrolyte solutions are very promising devices for practical applications. Only a few attempts have been undertaken to solve models with electrostatic forces, those have been restricted, moreover, to ionic fiuids with Coulomb interactions. We would hke to mention in advance that it is clear, at present, how to obtain the structural properties of ionic fiuids adsorbed in disordered charged matrices. Other systems with higher-order multipole interactions have not been studied so far. Thermodynamics of these systems, and, in particular, peculiarities of phase transitions, is the issue which is practically unsolved, in spite of its great importance. This part of our chapter is based on recent works from our laboratory [37,38]. 

The properties of platinum as an inert electrode in a variety of electrolytic processes are well known, and in cathodic protection it is utilised as a thin coating on a suitable substrate. In this way a small mass of Pt can provide a very large surface area and thus anodes of this type can be operated at high current densities in certain electrolyte solutions, such as seawater, and can be economical to use. 

In contrast chemical and electrolytic polishing enables a smooth level surface to be produced without any residual stress being developed in the surface because the surface is removed by dissolution at relatively low chemical potential and at relatively low rates is such a way that metallic surface asperities are preferentially removed. For this to be most effective the solution properties must be optimised and the pretreatment must leave an essentially bare metal surface for attack by the electrolyte. 

A second characteristic property of metals is high electrical conductivity. The conductivity is so much higher than that of aqueous electrolyte solutions that the charge movement cannot involve the same mechanism. Again we find a... 

In the last two decades experimental evidence has been gathered showing that the intrinsic properties of the electrolytes determine both bulk properties of the solution and the reactivity of the solutes at the electrodes. Examples covering various aspects of this field are given in Ref. [16]. Intrinsic properties may be described with the help of local structures caused by ion-ion, ion-solvent, and solvent-solvent interactions. An efficient description of the properties of electrolyte solutions up to salt concentrations significantly larger than 1 mol kg 1 is based on the chemical model of electrolytes. 

A method for determining partial molar properties, most often applied to electrolyte solutions, involves using the apparent molar property [Pg.222]

Calculation of the Thermodynamic Properties of Strong Electrolyte Solutes The Debye-Hiickel Theory... 

Chapters 7 to 9 apply the thermodynamic relationships to mixtures, to phase equilibria, and to chemical equilibrium. In Chapter 7, both nonelectrolyte and electrolyte solutions are described, including the properties of ideal mixtures. The Debye-Hiickel theory is developed and applied to the electrolyte solutions. Thermal properties and osmotic pressure are also described. In Chapter 8, the principles of phase equilibria of pure substances and of mixtures are presented. The phase rule, Clapeyron equation, and phase diagrams are used extensively in the description of representative systems. Chapter 9 uses thermodynamics to describe chemical equilibrium. The equilibrium constant and its relationship to pressure, temperature, and activity is developed, as are the basic equations that apply to electrochemical cells. Examples are given that demonstrate the use of thermodynamics in predicting equilibrium conditions and cell voltages. 

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