Kohlrausch's Law in Chemistry: Definition, Applications, and Importance
Chemistry, particularly physical chemistry, deals with the study of electrolytes and their behavior in solutions. One of the fundamental principles that help understand ionic conductivity in solutions is Kohlrausch’s Law. This law plays a critical role in determining the limiting molar conductivity of weak and strong electrolytes and has significant applications in electrochemistry.
What is Kohlrausch’s Law?
“At infinite dilution, the molar conductivity of an electrolyte is equal to the sum of the individual contributions of the cation and anion.”
Mathematical Expression
Λm° = λ°+ + λ°−
Applications of Kohlrausch’s Law
- Determination of molar conductivity of weak electrolytes
- Calculation of degree of dissociation
- Determination of dissociation constant
- Verification of ion conductance
- Determining solubility of sparingly soluble salts
20 IIT-Level Questions on Kohlrausch's Law
1. What is Kohlrausch’s Law of Independent Migration of Ions?
At infinite dilution, each ion contributes independently to the total molar conductivity of an electrolyte.
2. State the mathematical expression of Kohlrausch’s Law.
Λm° = λ°+ + λ°-
Numerical Problems on Kohlrausch's Law
1️⃣ Calculate Λ⁰(CH₃COOH) using: Λ⁰(CH₃COONa)=91, Λ⁰(HCl)=426, Λ⁰(NaCl)=126
Λ⁰ = 91 + 426 - 126 = 391 S·cm²/mol
2️⃣ If Λ=78 and Λ⁰=390, calculate degree of dissociation.
α = 78 / 390 = 0.2 or 20%
