Solutions of electrolytes, aqueous

In the past the emphasis in the study of solvation has been on what happens to the solute when it changes from the pure state to the dissolved state in the solvent. Obviously the chemist has been very much aware of the role of the solvent in solution, but the focus has always been on the solvated solute species. 

Experimental techniques for studying solvation include direct methods such as spectroscopic methods, diffraction techniques and light scattering. Use can also be made of indirect methods such as thermodynamic properties, conductance and activity coefficient studies, and diffusion. Computer simulation experiments have increasingly been playing a major role. 

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The measurement of change in the surface potentials of aqueous solutions of electrolytes caused hy adsorption of ionophore (e.g., crown ether) monolayers seems to he a convenient and promising method to ascertain selectivity and the effective dipole moments of the ionophore-ion complexes created at the water surface. 

As a result of these electrostatic effects aqueous solutions of electrolytes behave in a way that is non-ideal. This non-ideality has been accounted for successfully in dilute solutions by application of the Debye-Huckel theory, which introduces the concept of ionic activity. The Debye-Huckel Umiting law states that the mean ionic activity coefficient y+ can be related to the charges on the ions, and z, by the equation... 

Ionic activity essentially represents the concentration of a particular type of ion in aqueous solution and is important in the accurate formulation of thermodynamic equations relating to aqueous solutions of electrolytes (Barrow, 1979). It replaces concentration because a given ion tends not to behave as a discrete entity but to gather a diffuse group of oppositely charged ions around it, a so-called ionic atmosphere. This means that the effective concentration of the original ion is less than its actual concentration, a fact which is reflected in the magnitude of the ionic activity coefficient. 

Weissenbom PK, Pugh RJ (1996) Surface tension of aqueous solutions of electrolytes relationship with hydration, oxygen solubility, and bubble coalescence. J Colloid Interface Sci 184 550-553... 

Predicting Vapor-Liquid-Solid Equilibria in Multicomponent Aqueous Solutions of Electrolytes... 

For aqueous solutions of electrolytes, a concise method of tabulating such entropy data is in terms of the individual ions, because entropies for the ions can be combined to give information for a wide variety of salts. The initial assembling of the ionic entropies generally is carried out by a reverse application of Equation (7.26) that is, Af6m of a salt is calculated from known values of AfG and AfFT for that salt. After a suitable convention has been adopted, the entropy of formation of the... 

The blood plasma is an aqueous solution of electrolytes, nutrients, metabolites, proteins, vitamins, trace elements, and signaling substances. The fluid phase of coagulated blood is known as blood serum. It differs from the plasma in that it lacks fibrin and other coagulation proteins (see p. 290). 

Solutions of electrolytes in water do not belong to the group of solutions under discussion, since, in the formation of aqueous solutions of electrolytes, there is a chemical reaction between the ions formed and the water molecules, which changes both the enthalpy and the entropy of the solution. 

Other physical phenomena that may be associated, at least partially, with complex formation are the effect of a salt on the viscosity of aqueous solutions of a sugar and the effect of carbohydrates on the electrical conductivity of aqueous solutions of electrolytes. Measurements have been made of the increase in viscosity of aqueous sucrose solutions caused by the presence of potassium acetate, potassium chloride, potassium oxalate, and the potassium and calcium salt of 5-oxo-2-pyrrolidinecarboxylic acid.81 Potassium acetate has a greater effect than potassium chloride, and calcium ion is more effective than potassium ion. Conductivities of 0.01-0.05 N aqueous solutions of potassium chloride, sodium chloride, potassium sulfate, sodium sulfate, sodium carbonate, potassium bicarbonate, potassium hydroxide, and sodium hydroxide, ammonium hydroxide, and calcium sulfate, in both the presence and absence of sucrose, have been determined by Selix.88 At a sucrose concentration of 15° Brix (15.9 g. of sucrose/100 ml. of solution), an increase of 1° Brix in sucrose causes a 4% decrease in conductivity. Landt and Bodea88 studied dilute aqueous solutions of potassium chloride, sodium chloride, barium chloride, and tetra-... 

Mishchenko and Dymarchuk (111) have studied the integral heats of reaction of cellulose with both water and aqueous solutions of electrolytes. A notable maximum in the integral heat of reaction occurs at approximately 2.5m. The authors visualize this sharp maximum as caused by the different behavior above and below the concentration where all the water is intimately tied up as water of hydration. Thus, assuming for calcium chloride that the hydration number is 8 for both the calcium ion and for the chloride ion, a concentration of 2.52m corresponds to complete hydration of the ions. Hence, they suggest that definite hydration numbers exist. It may well be argued, however, that heat of reaction with standard cotton cellulose is a poor probe to choose for studying the aqueous environment. The idea of fixed total hydration of the ions appears a somewhat unlikely interpretation if for no other reason than... 

If the liquid junction is formed between two aqueous solutions of electrolytes containing many types of ions of different valency and at different concentrations, the electrochemical potentials of all species are linked by the Gibbs-Duhem equation ((A.21), Appendix A). For any moving species, the change of its electrochemical potential is caused by the change of its molar free energy G . 

In the third period, which ended in 1999 after the book VIG was published, various fluids had been studied strongly polar nonassociated liquids, liquid water, aqueous solutions of electrolytes, and a solution of a nonelectrolyte (dimethyl sulfoxide). Dielectric behavior of water bound by proteins was also studied. The latter studies concern hemoglobin in aqueous solution and humidified collagen, which could also serve as a model of human skin. In these investigations a simplified but effective approach was used, in which the susceptibility % (m) of a complex system was represented as a superposition of the contributions due to several quasi-independent subensembles of molecules moving in different potential wells (VIG, p. 210). (The same approximation is used also in this chapter.) On the basis of a small-amplitude libration approximation used in terms of the cone-confined rotator model (GT, p. 238), the hybrid model was suggested in Refs. 32-34 and in VIG, p. 305. This model was successfully employed in most of our interpretations of the experimental results. Many citations of our works appeared in the literature. 

O. Ya. Samoilov, Structure of Aqueous Solutions of Electrolytes and Hydration of Ions, Izdat. Akademii Nauk SSSR, Moscow, 1957 (in Russian). 

It was recently suggested that the van der Waals interactions of the ions with the system can explain the ion specific effects [13], and it was shown that by accounting for this interactions one can successfully predict the dependence of surface tension of aqueous solutions of electrolytes on their concentration [14,15], In the first pad of this article [7], it was shown that the ion-hydration interaction can also explain the surface tension behaviour. 

Table 4. Equivalent conductances of aqueous solutions of electrolytes... 

Kohlrausch discovered, in the last century, that the molar conductivity of aqueous solutions of electrolytes increases with dilution, and reaches a limiting value at very great dilutions. The increase of molar conductivity, in line with the Arrhenius theory, results from the increasing degree of dissociation the limiting value corresponds to complete dissociation. This limiting value of the molar conductivity is denoted here by A0 (the notation A C is also used), while its value at a concentration c will be denoted by Ac. The degree of dissociation can be expressed as the ratio of these two molar conductivities... 

Sometimes the problem of solvation may be reduced to the investigation of hydrogen-bonded systems of the type (AH "A) , that represent an important entity in aqueous solutions of electrolytes. These systems possess double-well proton potential curves, if the A-A distance is larger than about 2.4 x 10 m. Such a hydrogen bond is... 

As regards aqueous solutions of electrolytes, there has been some significant advance in the understanding of the dielectric behaviour of the hydration sheath around the ions. In the field of non-electrolyte solutions, no claim can yet be made that th e is good understanding. It is obvious that the data are still insufficient this is the fidd where measurements are most needed. 

Figure 42.2 shows a hypothetical polymeric NF membrane with carboxylic groups attached to the surface of the membrane, which is brought in contact with an aqueous solution of electrolytes. The presence of dissociated carboxylic groups on the membrane surface causes the occurrence of membrane charge. 

F. Franks, Aqueous Solutions of Electrolytes , in Water , Royal Society of Chemistry, London, 1983, Ch. 10, p. 57-68. 

The batteries just discussed are called dry cells because the water is not free, but absorbed in pastes. In contrast, the Daniell cell and the lead-acid battery use aqueous solutions of electrolytes, so they should be used in an upright position. 

I. Zaytsev, G. Aseyev Properties of Aqueous Solution of Electrolytes, CRC Press, Boca Raton, Ann Arbor, London, Tokyo (1992)... 

Midoux [371/1] compared and evaluated five publications, in which c or e was determined in aqueous solutions of electrolytes, and found that ... 

Eremenko, B.V. et al.. Stability of suspensions of alumina nanoparticles in aqueous solutions of electrolytes. Colloid J., 58, 436, 1996. 

The critical coagulation concentration for a colloid suspended in an aqueous solution of electrolyte is determined by those ions with charge opposite in sign to that of the colloidal particles, and is proportional to an inverse power of the valence of the ions. 

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