Question

Define limiting molar conductivity.

Hint:

Remember the notation: \[ \Lambda_m = \text{Molar Conductivity} \] \[ \Lambda_m^{\circ} = \text{Limiting Molar Conductivity} \] At infinite dilution, ionic interactions become negligible and molar conductivity attains its maximum value.

Answer 1

Step 1: Recall how molar conductivity varies with dilution.
As an electrolyte solution is diluted, interionic attractions weaken, ions move more freely, and molar conductivity $\Lambda_m$ increases. At sufficiently extreme dilution (infinite dilution) this increase reaches a maximum limiting value.
Step 2: Definition of limiting molar conductivity.
Limiting molar conductivity ($\Lambda_m^\circ$) is the molar conductivity of an electrolyte at infinite dilution, when interionic interactions become negligible and each ion contributes independently to the total conductivity.
Step 3: How it is determined and applied.
For strong electrolytes, $\Lambda_m^\circ$ is obtained by extrapolating the $\Lambda_m$ vs $\sqrt{C}$ graph to zero concentration. For weak electrolytes, Kohlrausch's law gives $\Lambda_m^\circ = \sum \lambda^\circ_{ions}$. It is used to find the degree of dissociation $\alpha = \Lambda_m / \Lambda_m^\circ$ of weak electrolytes.