Question 14 Marks
Define conductivity and molar conductivity for the solution of an electrolyte. Discuss their variation with concentration.
Answer
View full question & answer→Conductivity $(\kappa)$ : The inverse (opposite) of resistivity (or specific resistance) is called conductivity. It is also called specific conductivity. Its symbol is $\kappa$ and $\kappa=\frac{1}{\rho}$.
Or, The conductivity of the solution at a given concentration is the conductivity of its unit volume placed between two electrodes at unit cross-sectional area spaced at unit distance.
Molar conductivity ($\Lambda_{ m }$) : Molar conductivity is the conductivity of Volume V of the solution in which one mole of electrolyte is dissolved and which is placed between two electrodes of cross-sectional area A, located at a unit distance from each other.
Or, Molar conductivity is the conductivity of that volume of solution of an electrolyte which is placed between the electrodes located at unit distance of the conductivity cell and whose cross-sectional area is sufficient to hold the volume (V) of the solution in which the electrolyte is present. Therefore, the conductivity of ions obtained by dissolving one mole of electrolyte in solution is called molar conductivity.
Both conductivity and molar conductivity changes with change in concentration of electrolyte. Conductivity always decreases when concentration of both strong and weak electrolytes is reduced because on increasing dilution the number of ions carrying the number of ions carrying electric current per unit volume decreases.
Molar conductivity increases as the concentration decreases because the total volume (V) in which one mole of electrolyte is present increases $\left(\Lambda_{ m } \kappa V \right)$ and the increase in volume is greater than decrease in conductivity $(\kappa)$.
Or, The conductivity of the solution at a given concentration is the conductivity of its unit volume placed between two electrodes at unit cross-sectional area spaced at unit distance.
Molar conductivity ($\Lambda_{ m }$) : Molar conductivity is the conductivity of Volume V of the solution in which one mole of electrolyte is dissolved and which is placed between two electrodes of cross-sectional area A, located at a unit distance from each other.
Or, Molar conductivity is the conductivity of that volume of solution of an electrolyte which is placed between the electrodes located at unit distance of the conductivity cell and whose cross-sectional area is sufficient to hold the volume (V) of the solution in which the electrolyte is present. Therefore, the conductivity of ions obtained by dissolving one mole of electrolyte in solution is called molar conductivity.
Both conductivity and molar conductivity changes with change in concentration of electrolyte. Conductivity always decreases when concentration of both strong and weak electrolytes is reduced because on increasing dilution the number of ions carrying the number of ions carrying electric current per unit volume decreases.
Molar conductivity increases as the concentration decreases because the total volume (V) in which one mole of electrolyte is present increases $\left(\Lambda_{ m } \kappa V \right)$ and the increase in volume is greater than decrease in conductivity $(\kappa)$.