Ionic hydration theory

If ionic hydration theory is used as a basis for obtaining single-ion activity coefficients, somewhat different values result. For example, yci- values of 0.620 and 0.586 are obtained when NaCl and KCl are used. At an ionic strength of 0.1... 

The ionic hydration theory has been used to explain the effect of some ofthese factors on selectivity, According to this theory, the ions in aqueous... 

This simple hydration theory cannot explain all the known phenomena, as, for example, the opposite effects of calcium chloride and zinc chloride on the colours. Engel2 therefore assumed that the observed colours were due to certain double salts present in the solutions. In the case of pure cobalt chloride, hydrolysis was supposed to occur on heating the solution, the hydrochloric acid liberated uniting with unchanged cobalt chloride and as an explanation of the colour change this is almost certainly incorrect. Ostwald 3 suggested a simple ionic explanation, namely, that the red colour is that of the cobalt cation, and the blue that of the undissociated salt. This is certainly not a complete explanation, and seems to necessitate a very marked decrease in ionisation with rise of temperature, which experiment, so far, does not support.4... 

In order to test Eq. (3.130), which is a quantitative statement of the influence of ionic hydration on activity coefficients, it is necessary to know the quantity and the activity of water, it being assumed that an experimentally calibrated value of the ion size parameter is available. The activity of water can be obtained from independent experiments (Table 3.12). The quantity can be used as a parameter. If Eq. (3.130) is tested as a two-parameter equation (n and a being the two parameters Table 3.13), it is found that theory is in excellent accord with experiment. For instance, in the case of NaCl, the calculated activity coefficient agrees with the experimental value for solutions as concentrated as 5 mol dm" (Fig. 3.39). 

Problems, for student solution pure liquid electrolytes, 762 ionic solution theory, 352 micro research standard, 357 on hydration, 217 on molten salts, 758, 762 Radiotraca- detection of diffusion, 406 Raman effect, 84 Raman peaks, in various molten salts, 710 Raman lectra of chloro-gallates, 708 and ion solutions, 73... 

The Stokes-Robinson model was later modified by its creators for use in more concentrated solutions by accounting for dehydration equilibria (12). The original model was also modified by Nesbitt (12), who made the hydration number a decreasing function of the ionic strength. Other workers too numerous to mention here have also attempted to do something with hydration theory. 

Aqueous Solvation.—A review, covering the 1968—1972 publications, deals with physical properties, thermodynamics, and structures of non-aqueous and aqueous-non-aqueous solutions of electrolytes, and complete hydration limits. Thermodynamic aspects of ionic hydration also reviewed include the thermodynamic theory of solvation the molecular interpretation of ionic hydration hydration of gaseous ions (AG s, H s, and AA s) thermodynamic properties of ions at infinite dilution in water, solvent isotope effect in hydration reference solvents and ionic hydration and excess properties. A third review on the hydration of ions emphasizes the structure of water in the gaseous, liquid, and solid states the size of ions and the hydration numbers of ions and the structure of the hydrated shell from measurements of mobility, compressibility, activity, and from n.m.r. spectra. Pure water and aqueous LiCl at concentrations up to saturation have been examined by neutron and X-ray diffraction. For the neutron studies LiCl and D2O are employed. The data are consistent with a simple model involving only... 

The simplified lattice ion hydration theory describes surface charge development by nonreactive ionic solids placed in water. This theory applies to ionic solids that do not react with water to form weak surface acid groups (hydrolysis) and to ionic solids that do not undergo surface oxidation reactions. Either reaction type would modulate the surface charge that the solid develops in water. The only reaction of consequence then is the hydration of lattice ions, and the differential hydration of these lattice ions at the surface of the solid determines the sign of the surface charge. 

As was indicated earlier in this article, a detailed microscopic understanding of the phenomena underlying electrolysis took a very long time to mature and depended on postulation, proof and acceptance of such concepts as spontaneous ionization in solution, ionic hydration, free ion mobility in solution and the free-electron theory of metals. 

The main goal of the molecular dynamics computer simulation of ionic solvation and adsorption on a metal surface has been to test the above model and to provide more quantitative information about the different factors that influence the structure of hydrated ions at the interface. Unfortunately, most of the experimental information about these issues has been obtained from indirect measurements such as capacity and current-potential plots, although in recent years in situ experimental techniques have begun to provide an accurate test of the above model. For a recent review of experimental techniques and the theory of ionic adsorption at the water/metal interface, see the excellent paper by Philpott. ... 

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