as the dilution increases. When the concentration . . Strong electrolyte (KCI) Weak electrolyte (CH COOH) c (mol L - ) / m (S m mol – ) .
. Figure . Variation of molar conductance with concentration XII U9 Electro XII U9 Electro - - - - approaches zero, there is a sudden increase in the molar conductance and the curve is almost parallel to m Λ axis. This is due to the fact that the dissociation of the weak electrolyte increases with the increase in dilution (Ostwald dilution law).
Λ m values for strong electrolytes can be obtained by extrapolating the straight line, as shown in figure ( . ). But the same procedure is not applicable for weak electrolytes, as the plot is not a linear one, Λ m values of the weak electrolytes can be determined using Kohlraush's law. .
. 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 Λ Λ m m m A + B