Question

If the concentration of an electrolyte solution decreases, the molar conductivity \( \Lambda_m \) will:

• A. Decrease
• B. Increase
• C. Remain same
• D. Become zero

Hint:

Remember:

• Conductivity \( (\kappa) \) usually \textbf{decreases} on dilution.
• Molar conductivity \( (\Lambda_m) \) \textbf{increases} on dilution.

Answer 1

The Correct Option is B

Concept: Molar conductivity (\( \Lambda_m \)) is defined as the conducting power of all the ions produced by one mole of an electrolyte in solution. It is related to conductivity \( (\kappa) \) and concentration \( (C) \) by the relation: \[ \Lambda_m = \frac{\kappa \times 1000}{C} \] where

• \( \Lambda_m \) = Molar conductivity
• \( \kappa \) = Conductivity of the solution
• \( C \) = Concentration of electrolyte

On dilution, the distance between ions increases and interionic attraction decreases, allowing ions to move more freely.
Step 1: {Observe the mathematical relation.} \[ \Lambda_m = \frac{\kappa \times 1000}{C} \] From this relation, molar conductivity is inversely proportional to concentration.
Step 2: {Effect of decreasing concentration.} When concentration decreases: \[ C \downarrow \quad \Rightarrow \quad \Lambda_m \uparrow \] Therefore, molar conductivity increases.
Step 3: {Physical explanation.} On dilution:

• Interionic attraction decreases
• Ionic mobility increases
• Degree of ionization increases (especially for weak electrolytes)

Thus, molar conductivity increases with dilution. Hence, the correct option is (B) Increase.