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Define Conductivity and Molar Conductivity for the Solution of an Electrolyte. Discuss Their Variation with Concentration. - Chemistry

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ConceptConductance of Electrolytic Solutions Measurement of the Conductivity of Ionic Solutions

Question

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

Solution

Conductivity of a solution is defined as the conductance of a solution of 1 cm in length and area of cross-section 1 sq. cm. The inverse of resistivity is called conductivity or specific conductance. It is represented by the symbolκ. If ρ is resistivity, then we can write:

`k = 1/rho`

The conductivity of a solution at any given concentration is the conductance (G) of one unit volume of solution kept between two platinum electrodes with the unit area of cross-section and at a distance of unit length.

ie `G= k a/l = k.l =k`

Since a = 1, l = 1)

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 carry the current in a solution decreases with a decrease in concentration.

Molar conductivity:

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.

`Lambda_m = kA/l`

Now, l = 1 and A = V (volume containing 1 mole of the electrolyte).

`:.Lambda_m = kV`

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

The variation of `Lambda_m` with `sqrtc` for strong and weak electrolytes is shown in the following plot:

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Solution Define Conductivity and Molar Conductivity for the Solution of an Electrolyte. Discuss Their Variation with Concentration. Concept: Conductance of Electrolytic Solutions - Measurement of the Conductivity of Ionic Solutions.
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