Which mathematical equation describes the variation of molar conductivity (Λm) with concentration (C) for strong electrolytes in dilute solutions (the Debye-Hückel-Onsager equation)?
Answer and explanation
Correct answer: B. Λm = Λm° - A * sqrt(C)
- Step 1: For strong electrolytes, dissociation is complete at all concentrations, but interionic attractions (asymmetry and electrophoretic effects) retard ionic mobility at higher concentrations.
- Step 2: In dilute solutions, the relationship between molar conductivity and concentration is linear when plotted against .
- Step 3: The Debye-Hückel-Onsager equation is: , where is the limiting molar conductivity at infinite dilution and is a constant depending on solvent, temperature, and electrolyte type.
Answer
Λm = Λm° - A * sqrt(C)
Why not the others: 'Λm = Λm° + A C' falsely shows conductivity increasing with concentration; 'Λm = Λm° e^(-A C)' proposes an exponential decay unsupported by electrodynamics; 'Λm = Λm° / (1 + A sqrt(C))' is a non-linear hyperbolic form.
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