Question

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. Molar conductivity decreases sharply with increase in concentration.
• B. A small increase in molar conductivity is observed at infinite dilution.
• C. Molar conductivity increases sharply with increase in concentration.
• D. A small decrease in molar conductivity is observed at infinite dilution.

Hint:

At infinite dilution, the molar conductivity of weak electrolytes approaches a limiting value due to the complete dissociation of ions.

Answer 1

The Correct Option is A

Molar conductivity for a weak electrolyte generally shows a precipitous decline as concentration rises. This phenomenon is attributable to the following factors:

1. Molar Conductivity Defined: Molar conductivity (Λ_m) quantifies the conductivity of a solution relative to the electrolyte's molar concentration. It is calculated as:
Λ_m = κ/C
where κ represents conductivity and C denotes electrolyte concentration.

2. Weak Electrolyte Ionization Dynamics: Weak electrolytes exhibit incomplete ionization in solution. At elevated concentrations, the extent of ionization diminishes due to increased proximity of ions, leading to enhanced inter-ionic interactions and consequently, diminished ion mobility.

3. Impact of Concentration on Ion Interactions: Higher concentrations intensify ion-ion interactions. These electrostatic forces impede ion movement. Consequently, a reduced number of ions contribute to conductivity, thereby lowering molar conductivity.

4. Behavior at Infinite Dilution: At extreme dilutions (infinite dilution), ions are maximally separated, minimizing their interactions. This maximizes ion mobility, resulting in the highest achievable molar conductivity for the electrolyte.

In essence, an increase in weak electrolyte concentration leads to a pronounced decrease in molar conductivity, driven by amplified ion interactions and reduced ion mobility.