KOHLRAUSCH LAW OF INDEPENDENT MIGRATION OF IONS
In 1874, Kohlrausch formulated the law of independent migration of ions based on the
experimental data of conductivities of various electrolytes. This law can be stated as follows:
At infinite dilution, the dissociation of the electrolyte is complete and hence each ion makes definite
contribution to the equivalent conductivity of the electrolyte irrespective of the nature of other ions
associated with it.
Therefore the limiting equivalent conductivity of an electrolyte is the algebraic sum of limiting
equivalent conductivities of its constituent ions.
i.e., The limiting equivalent conductivity of an electrolyte, Λo
electrolyte
Where λo
+ and λo
– are the limiting equivalent conductivities of cation and anion respectively.
However the Kohlrausch law can also be stated in terms of molar conductivities as:
The limiting molar conductivity of an electrolyte is the sum of individual contributions of limiting
molar conductivities of its constituent ions.
i.e., The molar equivalent conductivity of an electrolyte, μo
electrolyte
Where μo
+ and μo
– are the limiting molar conductivities of cation and anion respectively.
And n+ and n- are the stoichiometric numbers of positive and negative ions formed during the
dissociation of electrolyte.
EXPERIMENTAL BASIS AND THEORETICAL EXPLANATION OF KOHLRAUSCH LAW
Kohlrausch observed that at infinite dilutions, the difference between the conductivities of
sodium and potassium salts is constant irrespective of the associated anions, as tabulated
In 1874, Kohlrausch formulated the law of independent migration of ions based on the
experimental data of conductivities of various electrolytes. This law can be stated as follows:
At infinite dilution, the dissociation of the electrolyte is complete and hence each ion makes definite
contribution to the equivalent conductivity of the electrolyte irrespective of the nature of other ions
associated with it.
Therefore the limiting equivalent conductivity of an electrolyte is the algebraic sum of limiting
equivalent conductivities of its constituent ions.
i.e., The limiting equivalent conductivity of an electrolyte, Λo
electrolyte
Where λo
+ and λo
– are the limiting equivalent conductivities of cation and anion respectively.
However the Kohlrausch law can also be stated in terms of molar conductivities as:
The limiting molar conductivity of an electrolyte is the sum of individual contributions of limiting
molar conductivities of its constituent ions.
i.e., The molar equivalent conductivity of an electrolyte, μo
electrolyte
Where μo
+ and μo
– are the limiting molar conductivities of cation and anion respectively.
And n+ and n- are the stoichiometric numbers of positive and negative ions formed during the
dissociation of electrolyte.
EXPERIMENTAL BASIS AND THEORETICAL EXPLANATION OF KOHLRAUSCH LAW
Kohlrausch observed that at infinite dilutions, the difference between the conductivities of
sodium and potassium salts is constant irrespective of the associated anions, as tabulated
