Question

Define Molar Conductivity and explain its variation with dilution for a strong electrolyte.

Hint:

{Strong electrolyte:} Small increase in molar conductivity with dilution Approaches limiting value at infinite dilution.

Answer 1

Concept: Molar conductivity is an important concept in electrochemistry that relates the conductivity of an electrolyte solution to the amount of electrolyte present. It helps in understanding the ionic behavior of electrolytes in solution. Definition: Molar conductivity (\(\Lambda_m\)) is defined as the conductance of a solution containing one mole of an electrolyte placed between two electrodes with unit area and unit distance apart. Mathematically, \[ \Lambda_m = \frac{\kappa}{C} \] where:

• \( \Lambda_m \) = molar conductivity
• \( \kappa \) = conductivity of the solution
• \( C \) = molar concentration of the electrolyte

Its unit is \( \text{S cm}^2 \text{ mol}^{-1} \). Variation with dilution for a strong electrolyte: Strong electrolytes are completely ionized in solution. However, molar conductivity still changes with dilution due to ionic interactions.

• Increase with dilution: As the solution is diluted, molar conductivity increases.
• Reason: Inter-ionic attractions decrease with dilution, allowing ions to move more freely.
• Small increase: The increase is relatively small compared to weak electrolytes because strong electrolytes are already fully dissociated.
• Limiting molar conductivity: At infinite dilution, molar conductivity approaches a maximum value called limiting molar conductivity (\(\Lambda_m^\circ\)).

Graphical representation: A plot of molar conductivity versus \(\sqrt{C}\) for strong electrolytes shows a linear increase as concentration decreases. Conclusion: Thus, molar conductivity increases slightly with dilution for strong electrolytes due to reduced inter-ionic interactions and increased ionic mobility.