Conductance of Electrolytic Solutions

topicmedium9 MCQ

Specific and molar conductivity, Kohlrausch's law and variation with dilution. (Chemistry › Electrochemistry, NEET UG syllabus.)

What is Conductance of Electrolytic Solutions?

The ease with which electric current flows through a conductor. It is the reciprocal of resistance.

Key formula / rule: Conductance

Define and differentiate between resistance, conductance, specific conductance, and molar conductivity.
Explain the factors affecting electrolytic conductance.
Describe and explain the variation of specific and molar conductivity with dilution for strong and weak electrolytes.
State Kohlrausch's Law of Independent Migration of Ions and its applications.

Confusing specific conductivity (κ) with molar conductivity (Λm) and their variation with dilution.

Term: Conductance
Meaning: The ease with which electric current flows through a conductor. It is the reciprocal of resistance.

Term: Specific Conductance (Conductivity)
Meaning: The conductance of a solution of unit length and unit cross-sectional area. It is the reciprocal of resistivity.

Term: Molar Conductivity
Meaning: The conductance of the volume of solution containing one mole of electrolyte placed between two electrodes with unit area of cross-section and a distance of unit length.

Term: Limiting Molar Conductivity (Λm°)
Meaning: The molar conductivity of an electrolyte at infinite dilution, where the dissociation is complete and interionic interactions are negligible.

Term: Cell Constant (G*)
Meaning: The ratio of the distance between the electrodes (l) to the area of cross-section of the electrodes (A) in a conductivity cell. G* = l/A.

Define and differentiate between resistance, conductance, specific conductance, and molar conductivity.
Explain the factors affecting electrolytic conductance.
Describe and explain the variation of specific and molar conductivity with dilution for strong and weak electrolytes.
State Kohlrausch's Law of Independent Migration of Ions and its applications.
Calculate limiting molar conductivity for weak electrolytes using Kohlrausch's Law.
Determine the ° of dissociation of weak electrolytes.

Name: Specific Conductance (Conductivity)
Note: κ is specific conductance, ρ is resistivity, G is conductance, l is length, A is area, G* is cell constant. Unit: S cm⁻¹ or S m⁻¹.
Expression: κ = 1/ρ = G × (l/A) = G × G*

Name: Molar Conductivity (SI units)
Note: Λm is molar conductivity, κ is specific conductance (S m⁻¹), C is molar concentration (mol m⁻³). Unit: S m² mol⁻¹.
Expression: Λm = κ / C

Name: Molar Conductivity (Common units)
Note: Λm is molar conductivity, κ is specific conductance (S cm⁻¹), M is molar concentration (mol L⁻¹). Unit: S cm² mol⁻¹.
Expression: Λm = (κ × 1000) / M

Name: Kohlrausch's Law
Note: Λm° is limiting molar conductivity, ν₊ and ν₋ are stoichiometric coefficients of cation and anion, λ°₊ and λ°₋ are limiting molar ionic conductivities.
Expression: Λm° = ν₊λ°₊ + ν₋λ°₋

Name: Degree of Dissociation
Note: α is ° of dissociation for a weak electrolyte, Λm is molar conductivity at concentration C, Λm° is limiting molar conductivity.
Expression: α = Λm / Λm°

Confusing specific conductivity (κ) with molar conductivity (Λm) and their variation with dilution.
Incorrectly applying Kohlrausch's Law, especially with stoichiometry (ν₊, ν₋).
Errors in unit conversions, particularly between S cm² mol⁻¹ and S m² mol⁻¹.
Assuming that specific conductivity increases with dilution for weak electrolytes (it decreases, but molar conductivity increases).
Not understanding why Λm increases with dilution for strong electrolytes (increased mobility outweighs decreased concentration).

Which of the following statements correctly describes the variation of molar conductivity (Λm) with dilution for both strong and weak electrolytes?…
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What is specific conductivity (κ) of an electrolytic solution?…
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How does specific conductivity (κ) of an electrolytic solution change upon dilution?…
easy