Question

Define conductivity and molar conductivity for a solution of an electrolyte. Why does the conductivity of a solution decrease with decrease in concentration?

Hint:

Conductivity ($\kappa$) always decreases with dilution, but Molar Conductivity ($\Lambda_m$) always increases with dilution.

Answer 1

Step 1: Concept
Definitions of physical quantities related to electrolytic conductance.

Step 2: Meaning
Conductivity ($\kappa$) measures the conductance of a unit volume. Molar conductivity ($\Lambda_m$) measures the conductance of all ions from one mole of electrolyte.

Step 3: Analysis
As a solution is diluted (concentration decreases), the total volume increases. Consequently, the actual number of charge-carrying ions present in exactly $1\text{ cm}^3$ of the solution decreases, causing an overall drop in conductivity.

Final Answer: Conductivity ($\kappa$) is the conductance of $1\text{ cm}^3$ of the solution of an electrolyte. Molar conductivity ($\Lambda_m$) is the conducting power of all the ions produced by dissolving one mole of an electrolyte in solution. Conductivity decreases with a decrease in concentration because the number of ions per unit volume responsible for carrying current decreases.