Question

Define conductivity and molar conductivity for the solution of an electrolyte. Discuss their variation with concentration.

Answer 1

Conductivity (K):

It is the conductance of unit cube of material. S.I unit is S/m. Common unit is S/cm.

The conductivity of an electrolytic solution always decreases with decrease in concentration that is on dilution. This is because with dilution, the degree of dissociation increases and the total number of current-carrying ions increases but the number of ions per unit volume decreases.

Molar conductivity Λ:

It is the ratio of the electrolytic conductivity k to the molar concentration C of the dissolved electrolyte.

Λ = \(\frac kC\)

It is also defined as the conductance of a volume of solution containing 1 mole of dissolved electrolyte when placed between parallel electrodes 1 cm apart and large enough to contain between them all the solution.

The S.I unit of molar conductivity is S m²/mol

The common unit of molar conductivity is S cm²/mol

The molar conductivity of strong and weak electrolytes increases with dilution (i.e, decrease in the concentration). This is because with dilution, the degree of dissociation increases and the total number of current-carrying ions increases.

Answer 2

Conductivity of a solution is defined as the conductance of a solution 1 cm in length and area of cross-section cm 2.1 is represented by K. 

Conductivity always decreases with a decrease in concentration both for weak and strong electrolytes. This is because the number of ions per unit volume that carries the current in a solution decreases with a decrease in concentration. 

Molar conductivity of a solution at a given concentration is the conductance of volume V of a solution containing 1 mole of the electrolyte kept between two electrodes with the area of cross-section A and distance of unit length. 

Molar conductivity increases with a decrease in concentration. This is because the total volume of the solution containing one mole of the electrolyte increases on dilution.