Walden's Rule

Walden's Rule

Walden's Rule

Walden's Rule

This empirical rule was suggested by P. Walden (1863–1957). According to this rule, the molar conductance of an electrolyte at infinite dilution is inversely proportional to the viscosity of the medium.
i.e. 位oM ∝ 1/畏
or, 位oM x 畏 = Constant
Where, 位oM is the molar conductance at infinite dilution and 畏 is the coefficient of viscosity of the solvent.
Thus, Walden's rule states that the product of coefficient of viscosity of a solvent and the equivalent conductance of an electrolyte at infinite dilution is approximately constant and independent of the nature of the solvent.
SolventsCH3OHCH3OCH3CH3CNC2H4Cl2CH3NO2C6H5NO2C6H5OH
oM 0.630.660.640.600.690.670.63
Walden's rule holds only for large ions such as tetra methyl ammonium ion (CH3)4N+ and the picrate ion C6H2(NO2)3O. However, if we exclude water, the smaller ions also obey Walden's rule, though not very satisfactorily because the smaller ions are more solvated than larger ions.