The Structure of Electrolytes

An electrolyte is a medium that is between the completely disordered gas and the well-ordered crystalline solid. Solutions have no long-range order, but a short-range order exists. This has been investigated by x-ray diffraction of water and of molten metals or by x-ray absorption spectroscopy (XAS). With decreasing temperature, one has an increasing 

High conductivity of H3O+ and OH ions via rearrangement of hydrogen bonds using the short-range order of water. 

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NMR Studies of the Structure of Electrolyte Solutions Covington, A. K. Newman, K. E 12... 

For a general review, see T. F. Young, F. F. MaranviUe, and H. M. Smith, Raman spectral investigations of ionic equihhria in solutions of strong electrolytes, in The Structure of Electrolytic Solutions, W. J. Hamer ed., Wiley, New York, 1959, pp. 35-63. 

A more detailed paper will be published in the monograph of the symposium of the Electrochemical Society on The Structure of Electrolytic Solutions, - held in Washington, May 1957. CL also Proc. Roy. Soc. A 1958 247 505. 

A new theory of electrolyte solutions is described. This theory is based on a Debye-Hiickel model and modified to allow for the mutual polarization of ions. From a general solution of the linearized Poisson-Boltzmann equation, an expression is derived for the activity coefficient of a central polarized ion in an ionic atmosphere of non-spherical symmetry that reduces to the Debye-Hiickel limiting laws at infinite dilution. A method for the simultaneous charging of an ion and its ionic cloud is developed to allow for ionic polarization. Comparison of the calculated activity coefficients with experimental values shows that the characteristic shapes of the log y vs. concentration curves are well represented by the theory up to moderately high concentrations. Some consequences in relation to the structure of electrolyte solutions are discussed. 

Note More extensive data in CW Davies. In WJ Hamer, ed. The Structure of Electrolytic Solutions. New York Wiley, 1959. 

The chloride ion is depicted as an unsolvated species in Eq. 1.6 because of experimental evidence that the residence time of a water molecule coordinated to Cl" is about 1 ps, the same as the residence time of the molecule in the structure of bulk water. See, for example, J. E. Enderby and G. W. Neilson, The structure of electrolyte solutions, Rep. Prog. Phys. 44 38 (1981). 

In summary, diffraction techniques provide a powerful means of investigating the structure of electrolyte solutions. They give information about the pair correlation functions which can be directly related to modern theoretical techniques such as molecular dynamics calculations. This information can also be used to improve the statistical thermodynamic models of electrolyte solutions discussed in chapter 3. 

Spedding, F. H. Atkinson, G. The Structure of Electrolytic Solutions (Ed.) W. J. Hamer, Chap. 22, John wiley, New York 1959... 

The interactions of equations 3 and 6 may be smaller or bigger than in 1. The structure of electrolyte solutions depends therefore in Hofmeister ion series on the specific ion-water interaction, on the coordination numbers and on the concentration if the hydration spheres are large enough to disturb each other. 

HAM] Hamer, W. J., The structure of electrolyte solutions, John Wiley and Sons, Inc., New York, Eds., (1959). Cited on page 253. 

The information on the structure of electrolyte solutions provided by thermwlynamic and transport properties on the one hand and by spectroscopic, relaxation and kinetic investigations on the other, complement one another with regard to the chemical model. Thermodynamic and transport properties provide the distance parameter R, the overall association constant Ka, and the activity coeffident y linked to it. No direct information can be achieved on the structure of the region a g r R and possible regions a Rj Rj. .. R. This problem, however, can be solved by modem spectroscopic and relaxation methods. 

Although the viscosity of an electrolytic solution is not a thermodynamic function, such data are frequently found in conjunction with the thermodynamic quantity. Kg, and the information which can be derived from accurate viscosity measurements is often useful in gaining an insight into the structure of electrolytic solutions. Consequently, it seems appropriate to digress momentarily and include a brief discussion of the subject in this section. 

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