Molar conductance

Molar Conductance

Definition: Molar conductance refers to the electrical conductivity offered by all the ions formed from one mole of an electrolyte dissolved in a specific volume of solution. It reflects the efficiency of an electrolyte in conducting electricity when fully dissociated.

Formula: Λ_m = κ × 1000 / C

• Λ_m = Molar conductance (S·cm²·mol⁻¹)
• κ = Specific conductance (S·cm⁻¹)
• C = Concentration of solution (mol·L⁻¹)

Units of Molar Conductance

• SI Unit: S·m²·mol⁻¹
• Common Unit: S·cm²·mol⁻¹ (1 S·m²·mol⁻¹ = 10,000 S·cm²·mol⁻¹)

Variation with Dilution

• Strong Electrolytes: Show a gradual increase in molar conductance with dilution and reach a maximum value at infinite dilution.
• Weak Electrolytes: Exhibit a sharp increase in molar conductance with dilution due to increased ionization.

Kohlrausch’s Law

At infinite dilution, the individual ions act independently, and their contributions to the overall molar conductance become additive.

Λ_m^⁰ = λ^⁰_+ve + λ^⁰_–ve

Applications

• To determine the degree of ionization of weak electrolytes.
• To calculate the dissociation constant (K_a or K_b).
• To differentiate between strong and weak electrolytes.
• To assess the level of purity in water or other solvents.

Molar conductance plays a key role in electrochemistry by providing insight into how ions behave, how well a solution conducts electricity, and the characteristics of different electrolytes.