# Chemistry Class 12 NCERT Solutions: Chapter 3 Electrochemistry Part 6

Q: 7. Define conductivity and molar conductivity for the solution of an electrolyte. Discuss their variation with concentration

Ans:

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 symbol is resistivity, then we can write:

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.

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.

Now, (Volume Containing 1 mole of the electrolyte).

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 with for strong and weak electrolytes is shown in the following plot:

Q: 8. The conductivity of M solution of at is. Calculate its molar conductivity.

Given,

∴ Molar conductivity,

Q: 9. The resistance of a conductivity cell containing solution at K is . What is the cell constant if conductivity of solution at is .

Ans:

Given,

Conductivity,

Resistance,

∴ Cell constant