Variation of molar conductivity with concentration

In respect of the variation of their conductances with concentration, strong and weak electrolytes show distinct characteristics. For strong electrolytes Kohlrausch established an empirical relationship between A and y/C, viz. 

Weak electrolytes show no such linear relationship. Their dissociation is considered to increase with increasing dilution of the solution so that the dissociation constant of a weak acid may be given as follows 

The last two relations are expressions of the Ostwald dilution law. For such electrolytes, Arrhenius showed that a, the degree of dissociation, may be given quite well by the following 

Ac being the measured molar conductivity at a finite electrolyte concentration. Such an expression is obviously meaningless for strong electrolytes where ionization is complete at all concentrations. A combination of Equations (4.6) and (4.7) gives 

In Table 4.1 the essential validity of the above expressions for determining dissociation constants is demonstrated. The values of K show fairly satisfactory constancy with concentration. 

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The variation of molar conductivity with concentration for a number of electrolytes is shown in Table 1.1. Because the conductance of solutions varies with temperature (at higher temperatures the conductance becomes higher), the temperature at which these conductances are measured must be given. Values shown on Table 1.1 were measured at 25°C. It can be seen from this table that while the variation of molar conductivity of some solutions with... 

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