Question

Given below are two statements :
Statement I : The limiting molar conductivity of KCl (strong electrolyte) is higher compared to that of \(CH_3COOH\) (weak electrolyte).
Statement II : Molar conductivity decreases with decrease in concentration of electrolyte.
In the light of the above statements, choose the most appropriate answer from the options given below :

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Hint:

Remember: Dilution always increases molar conductivity because the volume term dominates over the conductivity decrease. For limiting conductivities, \(H^+\) and \(OH^-\) have exceptionally high values due to the Grotthuss mechanism.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Limiting molar conductivity (\(\Lambda^\circ_m\)) depends on the individual ionic conductivities at infinite dilution. Molar conductivity (\(\Lambda_m\)) is the conducting power of all ions produced by one mole of an electrolyte in a given volume of solution.
Step 2: Detailed Explanation:
1. Analysis of Statement I: According to Kohlrausch's law, \(\Lambda^\circ_m\) is the sum of limiting ionic conductivities. The limiting ionic conductivity of \(H^+\) (\(\approx 349.6 \text{ S cm}^2 \text{ mol}^{-1}\)) is much higher than that of \(K^+\) (\(\approx 73.5 \text{ S cm}^2 \text{ mol}^{-1}\)). Because of this, \(\Lambda^\circ_m(CH_3COOH)\) is actually higher than \(\Lambda^\circ_m(KCl)\). Statement I is false.
2. Analysis of Statement II: Molar conductivity is defined as \(\Lambda_m = \frac{\kappa \times 1000}{M}\). As concentration decreases (dilution increases), the volume containing one mole of electrolyte increases. This increase in volume more than compensates for the decrease in \(\kappa\), leading to an increase in molar conductivity upon dilution for both strong and weak electrolytes. Statement II is false.
Step 3: Final Answer:
Both Statement I and Statement II are false.