Electrolytic Conductance

conductance that results from the presence in the electrolytes of positive and negative ions (cations and anions). The amount of total electricity transmitted by the cations and anions is referred to as the transport number. Electrolytic conductance is characterized quantitatively by the equivalent conductance Λ:

Λ = 1,000χ/c

where χ is the specific conductance of the solution in ohm^–1·cm^–1 and c is the concentration of the solution in gram equivalents per liter. The maximum value of Λ, which is equal to the sum of the equivalent conductances of the cations and anions, corresponds to a solution at infinite dilution, in which the molecules in the electrolyte are completely dissociated into ions.

The equivalent conductance of electrolytes decreases with increasing concentration of the solution. In solutions of weak electrolytes, Λ decreases rapidly with increasing c, primarily as a consequence of the decrease in ionic mobility and the degree of dissociation. In solutions of strong electrolytes, Λ decreases primarily as a result of the slowing down of the ions owing to the interaction of their charges, the intensity of the interaction increasing with concentration because of the decrease in the mean distance between the ions; Λ also decreases as a result of a decrease in ionic mobility upon an increase in the viscosity of the solution (seeMOBILITY OF IONS AND ELECTRONS). In extended electric fields, ionic mobility is so great that the ionic atmosphere (seeIONIC ATMOSPHERE), which hinders ionic mobility, has no time to form, and Λ increases sharply (the Wien effect). A similar phenomenon is observed upon the application of a high-frequency electric field to an electrolyte solution (the Debye-Falkenhagen effect).

The conductance of strong electrolytes is described satisfactorily by theoretical equations only for low concentrations, for example, by the Onsager equation of electrical conductivity.