Theories of Conductance The Non-ideal Case for Symmetrical Electrolytes

Theories of Conductance The Non-ideal Case for Symmetrical Electrolytes 

Chapter 11 focused attention on methods of analysing conductance data where the effects of non-ideality have been ignored, i.e. it has been assumed that there are no ionic interactions. The movement of ions in solution is then a result of motion induced by an applied potential gradient, i.e. an external field superimposed on random Brownian motion. The applied electric field will cause the positive ions to move in the direction of the field and anions to move in the opposite direction. The direction of the field is from the positive pole to the negative pole of the electrical system, and the field is set up by virtue of the potential drop between the two poles. 

Non-ideality has been shown to be due to ionic interactions between the ions and consideration of these led to the concept of the ionic atmosphere (see Sections 10.3 and 10.5). These interactions must be taken into account in any theory of conductance. Most of the theories of electrolyte conduction use the Debye-Hiickel model, but this model has to be modified to take into account extra features resulting from the movement of the ions in the solvent under the applied field. This has proved to be a very difficult task and most of the modern work has attempted many refinements all of which are mathematically very complex. Most of this work has focused on two effects which the existence of the ionic atmosphere imposes on the movement and velocity of the ions in an electrolyte solution. These are the relaxation and electrophoretic effects. 

Section 12.9 on post 1950 modem conductance theories for symmetrical electrolytes and Section 12.10 on Fuoss-Onsager s 1957 conductance equation for symmetrical electrolytes can be omitted until earlier sections are assimilated. These two sections deal with more up to date work which is able to be formulated in a straightforward analytical equation. The development behind these theories is complex and only a brief overview of the ideas behind these theories is given. Nonetheless the Fuoss-Onsager 1957 equation has been much used to analyse experimental data. How this is carried out in practice is given in Sections 12.10.1 to 

13 and this is now standard procedure and is relevant to anyone analysing conductance work. 

---

CH12 THEORIES OF CONDUCTANCE THE NON-IDEAL CASE FOR SYMMETRICAL ELECTROLYTES... 

CH12 THEORIES OF CONDUCTANCE THE NON-IDEAL CASE FOR SYMMETRICAL ELECTROLYTES Table 12.1 Approximate t values at various concentrations of a 1-1 electrolyte... 

---