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

Edited By Team Careers360 | Updated on Jul 01, 2022 05:54 PM IST

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°.

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Define Kohlrausch law.
Kohlrausch law: uses
History
Application Kohlrausch law
Solved Example

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

A method of calculating the dissociation degree
Salts that are sparingly soluble are calculated by their solubility
Electrolytes with a weak dissociation constant
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.

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Application Kohlrausch law

Electrolytes are dissociated by this constant to calculate their electrical conductivity.
A weak electrolyte limiting molar conductivity can be determined via this equation.
This law can also be used to determine the degrees of dissociation of weak electrolytes.
This law is also used to calculate the solubility constants of various salts.
Various electrochemical cells use it to calculate their potential as well.

NCERT Chemistry Notes:

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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Frequently Asked Questions (FAQs)

1. 1. Who discovered the law of the independent migration of ions?

A study of the conductivities of different electrolytes by Friedrich Kohlrausch led to the discovery of this law.

2. 2. What are the applications of Kohlrausch law of independent ion migration?

Weak electrolytes are calculated by applying this law by calculating their specific conductivity, dissociation constant, and degree of dissociation. Salt solubility can also be measured using this instrument.

3. 3. Ions migrate independently according to law?

Electrolytes limiting molar conductivity is determined by the relationship between its constituent ions and this law. After dilution, an electrolyte limiting molar conductivity is defined as the sum of the limiting molar conductivities of the ions it splits into.

4. 4. How was Kohlrausch law discovered?

As a result of Kohlrausch's experiments with dilute solutions, he discovered this law. His law was based on the observation that the difference in the limiting molar conductivity of two different electrolytes having the same anode (or cathode) is independent of the nature/type of the common anode (or cathode).

5. 5.Kohlrausch law of independent migration of ions explains this?

The limiting molar conductivity of an electrolyte is determined by the factor of the individual contributions of anion and cation. There is an additive effect in these contributions according to the Kohlrausch law.