Debye - Huckel and Onsager equation

Debye - Huckel and Onsager equation

We have learnt that at infinite dilution, the interaction between the ions in the electrolyte solution is negligible. Except this condition, electrostatic interaction between the ions alters the properties of the solution from those expected from the free – ions value. The influence of ion-ion interactions on the conductivity of strong electrolytes was studied by Debye and Huckel. They considered that each ion is surrounded by an ionic atmosphere of opposite sign, and derived an expression relating the molar conductance of strong electrolytes with the concentration by assuming complete dissociation. Later, the equation was further developed by Onsager. For a uni – univalent electrolyte the Debye Huckel and Onsager equation is given below.

Λ m = Î›0m âˆ’ ( A + B Î›0m ) âˆšC                          .....(9.12)

Where A and B are the constants which depend only on the nature of the solvent and temperature. The expression for A and B are

Here, D is the dielectric constant of the medium, Î· the viscosity of the medium and T the temperature in Kelvin.