Name: Equivalent Conductance
Uploaded: 2019-07-19
Duration: 4 min 34 s
Description: Equivalent conductance defined as the conductance of an electrolyte solution containing one gram equivalent of the electrolyte. Learn more through this video.

Question

How is molar conductivity of an aqueous solution of an electrolyte measured experimentally?

Accepted Answer

Molar conductivity of an aqueous solution of an electrolyte can be measured experimentally by using wheat stone bridge experiment and by using electrochemical cell.

The electrochemical cell consists of two platinum electrodes coated with platinum black. These electrodes have area of cross-section $A$ and are separated by a distance $l$ . The solution between these electrodes is equal to length of electrolyte $l$ and area of cross-section $A$ . The resistance of such column of solution is given by $R = ρ \times (\frac{l}{A})$ . The quantity $(\frac{l}{A})$ is called cell constant and is denoted by $G^{*}$ . The cell constant is determined by measuring the resistance of the cell containing a solution whose conductivity is already known.

Once the cell constant is determined, it can be used to measure resistance or conductivity of any solution. The given setup consists of two resistances $R_{3}, R_{4}$ a variable resistance $R_{1}$ and unknown resistance $R_{2}$ . An oscillator is connected to a bridge. $P$ is a detector of null point and the bridge is balanced when no current passes through the detector. Under these conditions, unknown resistance $R_{2} = \frac{R_{1} \times R_{4}}{R_{3}}$ .

Once the cell constant and the resistance is determined the conductivity of the solution is given by $κ = \frac{cell constant}{R} = \frac{G *}{R}$

The conductivity of solutions of different electrolytes in the same solvent and at a given temperature differs due to charge and size of the ions into which they dissociate. This type of conductivity is known as molar conductivity, and it is denoted by $Λ_{m}$ . It is related to the conductivity in the following way, $Λ_{m} = \frac{κ}{C} s m^{- 1}$ .

How is molar conductivity of an aqueous solution of an electrolyte measured experimentally?

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