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Kohlrausch's Law of Independent Migration of Ions: 

Kohlrausch determine ^0 values of pairs of some strong electrolytes containing same cation say KF and KCl, NaF and NaCl etc., and found that the difference in ^0  value in each case remains the same

^0m (KCl) - ^0m (KF) = ^0m (NaCl) - ^0m (NaF)

He also determined ^0 values of pairs of strong electrolytes containing same anion say KF and NaF, KCl and NaCl etc. and found that the difference in ^0 values is each case remains the same.

^0m (KF) - ^0m (NaF) = ^0m (KCl) - ^0m (NaCl)

This experimental data led him to formulate the following law called Kohlrausch's law of independent migration of ions.

Variation with Strong and Weak electrolytesVariation with Strong and Weak electrolytes

At infinite dilution when dissociation is complete, every ion makes some definite contribution towards molar conductance of the electrolyte irrespective of the nature of the other ion which with it is associated and that the molar conductance at infinite dilution for any electrolyte is given by the sum of the contribution of the two ions. Thus,

^0m+ + λ-o

Where λ0  is the contribution of the cation  is the contribution of the anion towards the molar conductance at infinite dilution. These contributions are called molar ionic conductances at infinite dilution. Thus, λ0  is the molar ionic conductance of cation and λ-o is the molar ionic conductance of anion, at infinite dilution. The above equation is, however, correct only for binary electrolyte like NaCl, MgSO4 etc.

Kohlrausch`s Law | Chemistry Class 12 - NEET


Application of Kohlrausch's law: 

(1) Determination of ^0m of a weak electrolyte: In order to calculate ^0m of a weak electrolyte say CH3COOH, we determine experimentally ^0m values of the following three strong electrolytes:

(a) A strong electrolyte containing same cation as in the test electrolyte, say HCl

(b) A strong electrolyte containing same anion as in the test electrolyte, say CH3COONa

(c) A strong electrolyte containing same anion of (a) and cation of (b) i.e. NaCl.

^0m of CH3COOH is the given as:

^0m (CH3COOH) = ^0m (HCl) + ^0m (CH3COONa) - ^0m (NaCl)

Proof :

^0m (HCl) = Kohlrausch`s Law | Chemistry Class 12 - NEET + Kohlrausch`s Law | Chemistry Class 12 - NEET ..................(i)

^0m (CH3COONa) = Kohlrausch`s Law | Chemistry Class 12 - NEET + Kohlrausch`s Law | Chemistry Class 12 - NEET ..................(ii)

^0m (NaCl) = Kohlrausch`s Law | Chemistry Class 12 - NEET + Kohlrausch`s Law | Chemistry Class 12 - NEET ..................(iii)

Adding equation (i) and equation (ii) and subtracting (iii) from them:

^0m (HCl) + Kohlrausch`s Law | Chemistry Class 12 - NEET

(2) Determination of degree of dissociation (α) :

α = Kohlrausch`s Law | Chemistry Class 12 - NEET

(3) Determination of solubility of sparingly soluble salt:

The specific conductivity of a saturated solution of the est electrolyte (sparingly soluble) made in conductivity water is determined by the method as described above. From this the specific conductivity of conductivity water is deducted.
The molar conductance of the saturated solution is taken to be equal to ^0m as the saturated solution of a sparingly soluble salt is extremely dilute. Hence from equation (4).

^0m = Kohlrausch`s Law | Chemistry Class 12 - NEET

Where C is the molarity of solution and hence the solubility.

ATLAS

Kohlrausch`s Law | Chemistry Class 12 - NEETKohlrausch`s Law | Chemistry Class 12 - NEET

The document Kohlrausch's Law | Chemistry Class 12 - NEET is a part of the NEET Course Chemistry Class 12.
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FAQs on Kohlrausch's Law - Chemistry Class 12 - NEET

1. What is Kohlrausch's Law?
Ans. Kohlrausch's Law, also known as the Kohlrausch's Law of Independent Migration of Ions, states that the conductivity of an electrolyte solution is directly proportional to the concentration of ions present in the solution. It explains the behavior of ions in a solution and their contribution to the overall conductivity.
2. How is Kohlrausch's Law applied in practice?
Ans. Kohlrausch's Law is widely applied in various fields, such as electrochemistry and analytical chemistry. It is used to determine the degree of dissociation of weak electrolytes, calculate the molar conductivity of electrolyte solutions, and study the conductance behavior of different ions in solution. This law enables scientists to understand the behavior of ions and their impact on the electrical conductivity of solutions.
3. What is the significance of Kohlrausch's Law in chemical analysis?
Ans. Kohlrausch's Law plays a crucial role in chemical analysis. By measuring the conductivity of solutions at different concentrations and temperatures, it allows chemists to determine the molar conductivity and degree of dissociation of electrolytes. This information is essential for understanding the nature of the electrolytes, their behavior in solution, and their ability to conduct electricity. Additionally, Kohlrausch's Law aids in the determination of unknown concentrations of ions in solutions.
4. How does temperature affect Kohlrausch's Law?
Ans. Temperature has a significant influence on Kohlrausch's Law. As the temperature increases, the conductivity of electrolyte solutions generally increases as well. This is due to the enhanced mobility of ions at higher temperatures. However, it is important to note that the effect of temperature on different electrolytes may vary. Some electrolytes may show an increase in conductivity with temperature, while others may exhibit a decrease or remain relatively constant.
5. Can Kohlrausch's Law be applied to non-aqueous solutions?
Ans. Yes, Kohlrausch's Law can be applied to non-aqueous solutions. While the law was initially formulated for aqueous solutions, it can also be extended to non-aqueous solvents. The principles behind the law remain the same, as it describes the behavior of ions in solution and their contribution to conductivity. However, it is important to consider the properties and behavior of the specific non-aqueous solvent being used, as they may affect the application of Kohlrausch's Law in these systems.
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