Electrolyte systems showing ion-pairing

We have seen that deviations from the Onsager equation in its limiting form occur for uni-univalent electrolytes at higher concentrations where observed molar conductivities are somewhat higher than predicted so that the slope of the A versus graph is somewhat lower than the theoretical Onsager slope. 

Deviations from the Onsager equation, shown by electrolytes with valency product 4 and 6, indicating ion-pairing. The dotted lines are the Onsager slopes. 

However, such deviations occur in the opposite sense to those obtained with low valency product electrolytes, i.e. observed conductances are now substantially lower than those predicted. Such deviations indicate a drastic reduction in the number of conducting species in solution, i.e. association to form ion-pairs has taken place. Such deviations become more marked in solvents of low dielectric constant. In such cases the conductance versus graph may show a minimum (Fig. 4.7) and this is attributed to the formation of triple ions which, unlike ion-pairs, carry a net charge. The formation of ion pairs removes two charged species from solution for each association which 

Plots of molar conductivity versus CI/2 for tetraisoamylammonium nitrate at various values of dielectric constant. 

---