Debye-Hiickel-Onsager Theory of Conductance

Changes to the Debye-Hiickel-Onsager Theory of Conductance 

Apart from improvements made by taking into account the fact that ions do indeed take up some of the space in electrolytic solutions, one has to consider also that ion association occurs in true electrolytes. 

What is the use of an empirical equation such as Eq. (4.326) It acts as a hanger for the facts. One fits experimental data of / as a function of c to the equation and determines by a least-squares fitting procedure the values of /1° and 

On the basis of tois model, Lee and Wheaton arrived at an equation for in terms of q, the Bjerrum distance. The equation is several lines long and clearly only fit for use in appropriate software. The application of experimental data of to the equation allows one to find values of and the co-sphere radius R. These values 

Another approach to the conductance of electrolytes, which is less complex than that of Lee and Wheaton, is due to Blum and his co-workers. This theory goes back to the original Debye-Hiickel-Onsager concepts, for it does not embrace the ideas of Lee and Wheaton about the detailed structure around the ion. Instead, it uses the concept of mean spherical approximation of statistical mechanics. This is the rather portentous phrase used for a simple idea, which was fully described in Section 3.12. It is easy to see that this is an approximation because in reality an ionic collision with another ion will be softer than the brick-wall sort of idea used in an MSA approach. However, using MSA, the resulting mathematical treatment turns out to be relatively simple. The principal equation from the theory of Blumet al. is correspondingly simple and can be quoted. It runs 

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When the ions in solvent are forced to move by an external field two effects start to influence conductance. The ions of opposite charge move in opposite directions and their movement is slowed down by the collision of the ionic atmosphere with the solvent molecules. The symmetry of ion distributions is disturbed. These phenomena are called the electrophoretic effect and relaxation effect, respectively. The decrease in conductance resulting from both effects is the basis of the Debye-Hiickel-Onsager theory of conductance [31]... 

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