Ionic Conductivity in Low-Temperature Molten Salts and Concentrated Solutions

  • Stuart I. Smedley


The Debye-Hückel theory of electrolyte solutions, based on the primitive continuum model, becomes invalid for aqueous 1: 1 electrolyte solutions at about 0.001 mol dm-3.(1) Above this concentration the ionic atmosphere of an ion, i.e., its electrical image in the solution, is closer to the ion than its nearest neighbors—a physical absurdity. However, the modified Debye-Hückel theory, with a suitable value of a fits the activity coefficient data up to about 0.1 mol dm-3.(3) Fuoss and Onsager, using a similar argument to that above, consider that their 1957 conductivity equation will be valid up to about 0.02 mol dm-3.(3) Above this concentration the electrical image of an ion (equal to unit charge) approaches closer than 7a, and large fluctuations would result in the potential at the central ion on the close approach of a near neighbor. This would invalidate a fundamental postulate of the Debye-Hückel theory, that the potential at the surface of the ion is related, by Poisson’s equation, to the average charge density surrounding the ion. However, Fuoss’s new theory (Chapter 2) is limited to 0.09 mol dm-3 for aqueous 1: 1 electrolytes and 0.002 mol dm-3 for 2: 1 electrolytes. (4) At these concentrations it becomes impossible to define uniquely an ion pair because three ion interactions become significant. In this theory ions that come within R > a are counted as paired and are excluded from the calculation of long-range effects.


Ionic Liquid Molten Salt Configurational Entropy Electrical Image Free Volume Theory 
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Copyright information

© Plenum Press, New York 1980

Authors and Affiliations

  • Stuart I. Smedley
    • 1
  1. 1.Victoria University of WellingtonWellingtonNew Zealand

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