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

Q7:Define conductivity and molar conductivity for the solution of an electrolyte. Discuss their variation with concentration.

Solution:

Conductivity :–

Conductivity of a solution is equal to the conductance of a solution of 1 cm length

and cross section area of 1 square cm.  it may also be define as the conductance of ine centimeter cube of the conductor . It is represented by the symbol Kappa (κ). mathematically we can write

κ = 1/ p

here ρ is resistivity

the unit of K is ohm ^–1 cm ^–1 or S cm^–1

The conductivity, κ, of an electrolytic solution depends on the concentration of the electrolyte, nature of solvent and temperature.

Molar conductivity:

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

Distance is unit  so l = 1

Volume          = area of base × length

So V   = A × 1  = A

Λ_m       =κA/l

Λ_m       = κV

Or

Molar conductivity increases with decrease in concentration. When concentration approaches zero, the molar conductivity is known as limiting molar conductivity and is represented by the symbol Ë^om.

For strong electrolytes, Λ increases slowly with dilution and can be represented by the equation:

Λ_m = Ë°_m° – A c ^½

conductivity and molar conductivity graph

It can be seen that if we plot Λm against c1/2, we obtain a straight line with intercept equal to Ë_m° and slope equal to ‘–A’. The value of the constant ‘A’ for a given solvent and temperature depends on the type of electrolyte i.e., the charges on the cation and anion produced on the dissociation of the electrolyte in solution.