The molar conductivity of a weak electrolyte when plotted against the square root of its concentration, which of the following is expected to be observed?
A small decrease in molar conductivity is observed at infinite dilution.
A small increase in molar conductivity is observed at infinite dilution.
Molar conductivity increases sharply with increase in concentration.
Molar conductivity decreases sharply with increase in concentration.
Correct answer:A
Standard Method
Given: The behavior of molar conductivity of a weak electrolyte is to be identified when plotted against the square root of concentration.
Find: Which observation is correct.
For a weak electrolyte, molar conductivity increases markedly on dilution because dissociation increases. Hence, with increase in concentration, the molar conductivity decreases sharply.
The solution states that at infinite dilution the ions are far apart, ion interaction is minimum, and molar conductivity attains its highest value.
Also,
So, as concentration increases for a weak electrolyte, reduced ionization and stronger ion-ion interactions cause a sharp decrease in molar conductivity.
Therefore, the correct option is D.
Discrepancy note: The source solution concludes Option A, but its explanation supports Option D. Based on the solution working, D is the most defensible answer.
Confusing weak electrolytes with strong electrolytes. Strong electrolytes show only a small change in molar conductivity with dilution, but weak electrolytes show a sharp change because their degree of dissociation changes significantly. Use the weak-electrolyte behavior here.
Interpreting infinite dilution incorrectly. Infinite dilution gives the maximum molar conductivity, not a decrease at that point. Always relate dilution to increased ionic mobility and dissociation for weak electrolytes.
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