Kohlrausch Law - Definition, Examples, Application & Uses, FAQs

Define Kohlrausch law.

In principle, an electrolyte's equivalent conductivity is equal to the sum of its anions and cations at infinite dilution, according to Kohlrausch law. When the concentration of a solution decreases, its molar conductivity increases. As the molecular conductivity of an electrolyte increases, the total volume containing a mole increase molar conductivity diminishes towards zero when the concentration of the electrolyte is zero; this condition is called limiting molar conductivity, Ëm°.

The limiting molar conductivities of several strong electrolytes were observed by Kohlrausch to show certain patterns. Using his observations as the basis, Kohlrausch proposed that "limiting molar conductivity can be modelled as a sum of the contributions of anions and cations in the electrolyte". Ions migrate independently according to the Kohlrausch law, popularly known. Identifying sodium

chloride's limiting molar conductivity, for instance, requires knowledge of sodium ions and chloride ions ' limiting molar conductivities. The Kohlrausch law of independent migration of ions has the following applications:

Our ability to determine the limiting molar conductivities of electrolytes is greatly aided by Kohlrausch law. At high concentrations, weak electrolytes exhibit lower molar conductivities and dissociation rates. Weak electrolytes exhibit a steep rise in molar conductivity with increasing concentration. As a result, limiting molar conductivity cannot be derived from extrapolating molar conductivity to zero concentration.

For weak electrolytes, we apply the Kohlrausch law of ion migration independently for determining limiting conductivity. Kohlrausch law formula provides a measure for weak electrolyte's molar conductivity, as well as to determine the dissociation constant and limit the conductivity.

α = Λ/ Ëm∘

Where, α = dissociation constant

Λ = molar conductivity

Ëm° = limiting molar conductivity

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Kohlrausch law: uses

1. A method of calculating the dissociation degree

2. Salts that are sparingly soluble are calculated by their solubility

3. Electrolytes with a weak dissociation constant

4. An infinite-dilution molar conductivity calculation for weak electrolytes

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History

The Kohlrausch law was introduced by Friedrich Kohlrausch in 1875-1879. He was an influential researcher of electrochemistry during his time as well as in the development of physical chemistry. It was chemists like Arrhenius, Ostwald, and Can’t Hoff who used the law of independent migration in order to formulate the Ironist theory, which is the basis of physical chemistry.

Application Kohlrausch law

1. Electrolytes are dissociated by this constant to calculate their electrical conductivity.

2. A weak electrolyte limiting molar conductivity can be determined via this equation.

3. This law can also be used to determine the degrees of dissociation of weak electrolytes.

4. This law is also used to calculate the solubility constants of various salts.

5. Various electrochemical cells use it to calculate their potential as well.

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Solved Example

Q1. Considering CH₃COOH as an electrolyte with weak conductivity, calculate its limiting molar conductivity?

At infinite dilution, CH₃COONa, HCl and NaCl have conductivities of 90.1S.cm²/mol, 426.16S.cm²/mol and 126.45S.cm²/mol respectively.

Solution.

Given,

λ∞_CH3COONa= 90.1S.cm²/mol

λ∞ _HCL=426.16S.cm²/mol

λ ∞_NaCl=126.45S.cm²/mol

According to Kohlrausch law of independent migration of ions,

λ∞_CH3COOH=λ∞_CH3COONa+λ∞_HCL–λ∞ _NaCl

λ∞_CH3COOH=91+426.16–126.45=>

λ∞_CH3COOH=390.71S.cm²/mol

So, the limiting molar conductivity of Acetic acid (CH₃COOH) is 390.71S.cm²/mol.

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