Choose the correct statement about molar conductivity, $Λ_m$

As the concentration of a weak electrolyte approaches zero, there is a sharp increase in the molar conductivity of the solution

The correct answer is Option (3) → As the concentration of a weak electrolyte approaches zero, there is a sharp increase in the molar conductivity of the solution

Molar conductivity (Λm) is defined as the conductance of the volume of solution containing one mole of electrolyte placed between two electrodes.

It is expressed as:

Λm = κ / c

where

κ = conductivity of the solution

c = concentration of electrolyte

When a solution is diluted, the distance between ions increases and interionic attraction decreases, allowing ions to move more freely.

For weak electrolytes, dilution causes a significant increase in ionization (degree of dissociation) according to Ostwald’s dilution law. As more molecules ionize, the number of charge-carrying ions increases rapidly.

Therefore, as the concentration approaches zero (infinite dilution), the molar conductivity of weak electrolytes increases sharply.

Option-wise Explanation

Option 1

Molar conductivity of a weak electrolyte decreases gradually as the concentration of the electrolyte decreases in the higher concentration ranges

This is incorrect. When concentration decreases (dilution increases), molar conductivity increases, not decreases, because ion mobility increases and weak electrolytes ionize more.

Option 2

Molar conductivity of a strong electrolyte increases linearly with the increase in the concentration of the electrolyte.

This is incorrect. For strong electrolytes, molar conductivity decreases with increase in concentration due to stronger interionic attractions. Also, the relationship is not linear with concentration.

Option 3

As the concentration of a weak electrolyte approaches zero, there is a sharp increase in the molar conductivity of the solution.

This is correct. Weak electrolytes ionize more upon dilution, producing more ions and leading to a sharp rise in molar conductivity near infinite dilution.

Option 4

The limiting molar conductivity of a weak electrolyte can be determined directly from the plot of Λm against c¹ᐟ²

This is incorrect. The Λm vs √c plot method is applicable to strong electrolytes. For weak electrolytes, the limiting molar conductivity is determined using Kohlrausch’s law of independent ionic migration, not directly from the plot.