Fundamental Problems in Pure Liquid Electrolytes

The first problem can be defined as follows What idealized model could best replicate a solvent-free system of charged particles forming a highly conducting ionic liquid In the case of the aqueous solution, it was easy to understand the drift of ions at the behest of the applied electric field. Positive and negative ions separated by large 

Properties Water at 298 K Liquid Sodium at m.p. 1 M Sodium Chloride Soln. at 298 K Liquid Sodium Chloride at m.p. Liquid Sodium Silicate near the m.p. 

What is the essential difference between the solid form and the liquid form of an ensemble of particles This is a question that is relevant to all processes of fusion, e.g., the process of solid argon melting to form a liquid. In the case of ionic liquids, the problem is more acute. One must explain the great fluidity and corresponding high conductivity in a liquid that contains only charged particles in contact. 

The second problem concerns an understanding of the sharing of transport duties (e.g., the carrying of current) in pure liquid electrolytes. In aqueous solutions, it was possible to comprehend the relative movements of ions in the sense that one ionic species could drift under an electric field with greater agility and therefore transport more electricity than the other until a concentration gradient was set up and the resulting diffusion flux equalized the movements when the electrodes were reached. In fused salts, this comprehension of the transport situation is less easy to acquire. At first, it is even difficult to see how one can retain the concept of transport numbers at all when there is no reference medium (such as the water in aqueous solutions) in which ions can drift. 

there exists another problem, that of complex ions. In aqueous and nonaqueous solutions, it is possible to regard the ionic atmosphere as a type of incipient complex in which the mean distance between oppositely charged ions becomes smaller with increasing electrolyte concentration. Eventually the ions come sufficiently close so that the thermal forces that tend to separate them are overcome on an increasingly frequent basis by the Coulombic attraction forces so that cation and anion pairs arise, some of which remain stuck together (see Section 3.8). 

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