Question

With reference to the variation of molar conductivity (\( \Lambda_m \)) with concentration for a strong electrolyte in an aqueous solution, the CORRECT statement is

• A. The asymmetry effect contributes to decrease \( \Lambda_m \) whereas the electrophoretic effect contributes to increase \( \Lambda_m \)
• B. The asymmetry effect contributes to increase \( \Lambda_m \) whereas the electrophoretic effect contributes to decrease \( \Lambda_m \)
• C. Both asymmetry effect and electrophoretic effect contribute to decrease \( \Lambda_m \)
• D. Both asymmetry effect and electrophoretic effect contribute to increase \( \Lambda_m \)

Hint:

The asymmetry effect tends to increase molar conductivity, while the electrophoretic effect tends to decrease it due to ion interactions in solution.

Answer 1

The Correct Option is C

Understanding molar conductivity (Λₘ) for strong electrolytes:

For strong electrolytes in aqueous solution, molar conductivity varies with concentration due to two main effects:

1. Asymmetry Effect (Relaxation Effect):

• When an ion moves under an applied field, it creates an asymmetric distribution of surrounding ions
• The ionic atmosphere is distorted and takes time to relax back to equilibrium
• This asymmetry opposes ion movement
• Decreases Λₘ

2. Electrophoretic Effect:

• The ionic atmosphere moves in the opposite direction to the central ion
• This creates a "drag" effect on the central ion
• The movement of surrounding ions and solvent in opposite direction slows down the central ion
• Decreases Λₘ

Concentration dependence:

As concentration increases:

• Ionic atmosphere becomes more dense
• Both asymmetry and electrophoretic effects become stronger
• Both effects work to decrease molar conductivity

Debye-Hückel-Onsager equation: $$\Lambda_m = \Lambda_m^0 - (A + B\Lambda_m^0)\sqrt{c}$$

where the negative term shows that both effects decrease Λₘ with increasing concentration.

Answer: (C) Both asymmetry effect and electrophoretic effect contribute to decrease Λₘ