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Question -

Define conductivity and molarconductivity for the solution of an electrolyte. Discuss their variation withconcentration.



Answer -

Conductivity of a solution isdefined as the conductance of a solution of 1 cm in length and area ofcross-section 1 sq. cm. The inverse of resistivity is called conductivity orspecific conductance. It is represented by the symbol╬║. If ╧Б isresistivity, then we can write:

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

i.e.,┬а

(Since┬аa┬а=1,┬аl┬а= 1)

Conductivity always decreaseswith a decrease in concentration, both for weak and strong electrolytes. Thisis because the number of ions per unit volume that carry the current in asolution decreases with a decrease in concentration.

Molar conductivity:

Molarconductivity of a solution at a given concentration is the conductance ofvolume V of a solution containing 1 mole of the electrolyte kept between twoelectrodes with the area of cross-section┬аA┬аand distance ofunit length.

Now,┬аl┬а= 1and┬аA┬а= V (volume containing 1 mole of the electrolyte).

Molar conductivity increases witha decrease in concentration. This is because the total volume V of the solutioncontaining one mole of the electrolyte increases on dilution.

Thevariation of┬аwithfor strong and weak electrolytes is shown in thefollowing plot:

┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а ┬а

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