About Lesson

__Arrangement for measurement of Resistance__

__Arrangement for measurement of Resistance__

- The arrangement consists of two resistances
*R*_{3}and*R*_{4}. - There is a variable resistance
*R*_{1}and a conductivity cell with unknown resistance*R*_{2}. - The Wheatstone bridge is provided with an oscillator O that acts as source of a.c. power.
- The arrangement has a suitable detector P.
- The Wheatstone bridge is balanced when there is no flow of current through the detector.

Unknown resistance = R_{2} = R_{1}R_{4} /R_{3}

- After calculating the resistance the conductiviry can be easily calculated using the formula:
- κ = G’ /R

__Molar conductivity__

__Molar conductivity__

- It is denoted by the symbol
*.*It is related to the conductivity of the solution by the following equation:

- The units of is S m
^{2 }mol^{-1}.

**Problem:**

### THE CONDUCTIVITY OF 0.20 M SOLUTION OF KCL AT 298 K IS 0.0248 SCM^{-1}. CALCULATE ITS MOLAR CONDUCTIVITY.

**Solution:**

*k* = 0.0248 S cm ^{– 1}

c = 0.20 M

Molar conductivity,Λ_{m} = (*k x 1000) / c*

= 0.0248 x1000 / 0.20

= 124 Scm^{2 }mol ^{– 1}

__Variation of Conductivity and Molar Conductivity with Concentration__

__Variation of Conductivity and Molar Conductivity with Concentration__

- They depend on the concentration of the electrolyte. The Conductivity and Molar Conductivity of both weak and strong electrolytes decreases withdecrease in concentration as the number of ions per unitvolume carrying the current in a solution decreases on dilution.

- Conductivity of a solution at a specific concentration = Conductance of solution placed in between the two platinum electrodes where
- Volume of solution = 1 unit

Cross sectional area of electrodes = 1unit