Kohlrausch’s Law of Independent Migration

Some applications of Kohlrausch’s law of independent migration of ions are:

Kohlrausch’s Law of Independent Migration of Ions can be represented graphically by plotting an electrolyte’s molar conductivity (λm) against the square root of its concentration (√c). According to Kohlrausch’s Law, the plot should be a straight line with an intercept equal to the limiting molar conductivity (λ∞m) and a slope similar to -A, where A is a constant.

The value of A depends on the type of electrolyte and the temperature at which the measurement is taken. The graph obtained by plotting λm against √c helps determine the limiting molar conductivity of weak electrolytes, which cannot be obtained by extrapolation of molar conductivity to zero concentration. The value of λ∞m can be determined from the intercept of the straight line obtained from the plot. The graph can also be used to calculate the degree of dissociation and dissociation constant of weak electrolytes.

At lower concentrations, weak electrolytes exhibit a steep increase in molar conductivity. Therefore, extrapolating molar conductivity to zero concentration will not yield Λ, the limiting molar conductivity. Consequently, we calculate the limiting molar conductivity for weak electrolytes, Λ, using the Kohlrausch law of independent ion migration.

For a weak electrolyte at a particular concentration, Kohlrausch’s law also aids in calculating the dissociation constant from the molar conductivity and limiting molar conductivity values.

α = Λ/Em°

where,

• α is Dissociation Constant
• Λ is Molar Conductivity
• Em° is Limiting Molar Conductivity

Kohlrausch’s law, also known as the law of Independent migration of Ions, tells us that the total of the limiting molar conductance of cations and anions of an electrolyte is equal to the molar conductivity of that electrolyte. This law helps us study electrochemical cells and diluted liquids and is applicable in determining weak electrolytes’ molar conductivity.

In this article, we will learn the concepts of Kohlrausch law, its applications, etc. We have to study Kohlrausch Law in Class 12 for board exams.