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

**Answer:**

**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

Λm =κA/l

Λm = 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°m.

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

Λm = Ë°m° – A c ^{½}

It can be seen that if we plot Λm against c1/2, we obtain a straight line with intercept equal to Ëm° 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.