Doc: Conductance of Electrolytic Solutions Class 12 Notes | EduRev

Chemistry Class 12

Created by: Mohit Rajpoot

Class 12 : Doc: Conductance of Electrolytic Solutions Class 12 Notes | EduRev

The document Doc: Conductance of Electrolytic Solutions Class 12 Notes | EduRev is a part of the Class 12 Course Chemistry Class 12.
All you need of Class 12 at this link: Class 12

Conductance 

Introduction: 

Both metallic and electrolytic conductors obey Ohm's law

i.e. V = IR

where V = Potential difference in volt; I Current in ampere ; R = resistance in Ohm

We know, resistance is directly proportional to length of conductor and inversely proportional to cross sectional area of the conductor.

Doc: Conductance of Electrolytic Solutions Class 12 Notes | EduRev 

Specific resistance is the resistance of a conductor having lengths of 1 cm and cross sectional area of 1 cm2.

Unit of R is ohm and unit of specific resistance is ohm cm

Reciprocal of resistance is called as conductance and reciprocal of specific resistance is called as specific conductance. 

Doc: Conductance of Electrolytic Solutions Class 12 Notes | EduRev

where C = conductance ohm-1; K = specific conductance ohm-1 cm-1.

Ohm and siemens are other units of conductance.

Doc: Conductance of Electrolytic Solutions Class 12 Notes | EduRev

Specific conductance = Cell constant x Conductance.

Specific Conductance is Conductance of 1 cm3 of an electrolyte solution.

In case of electrolytic solution, the specific conductance is defined as the conductance of a solution of definite concentration enclosed in a cell having two electrodes of unit area separated by 1 cm apart.

1. Equivalent Conductance 

Equivalent conductance is the conductance of an electrolyte solution containing 1 gm equivalent of electrolyte. It is denoted by ^.

^ = K × V

( ^ = ohm-1 cm-1 × cm3 = ohm-1 cm2)

Usually concern ration of electrolyte solution is expresses as C gm equivalent per litre.

Thus, V = Doc: Conductance of Electrolytic Solutions Class 12 Notes | EduRev

{Volume having 1 gm equivalent electrolyte in the solution} Thus, ^ = K × Doc: Conductance of Electrolytic Solutions Class 12 Notes | EduRev.

2. Molar Conductance

Molar conductance may be defined as conductance of an electrolyte solution having 1 gm mole electrolyte in a litre. It is denoted by ^m.

^m = K × V

Usually concentration of electrolyte solution is expressed as 'M' gm mole electrolyte per litre.

Thus, V = Doc: Conductance of Electrolytic Solutions Class 12 Notes | EduRev 

Hence, ^m = K × Doc: Conductance of Electrolytic Solutions Class 12 Notes | EduRev

Relation between ^ and ^m^m = n × ^

Determination of ^m0 or ^0 

A plot of ^m vs as found experimentally is as shown below graphically.

Doc: Conductance of Electrolytic Solutions Class 12 Notes | EduRev

the ^m vs Doc: Conductance of Electrolytic Solutions Class 12 Notes | EduRev plot of strong electrolyte being linear it can be extrapolated to zero concentration.

Thus, ^m values of the solution of the test electrolyte are determined at various concentrations the concentrations should be as low as good.

^m values are then plotted against Doc: Conductance of Electrolytic Solutions Class 12 Notes | EduRev when a straight line is obtained. This is the extrapolated to zero concentration. The point where the straight line intersects ^m axis is ^ºm of the strong electrolyte.

However, the plot in the case weak electrolyte being non linear, shooting up suddenly at some low concentration and assuming the shape of a straight line parallel to ^m axis. Hence extrapolation in this case is not possible. Thus, ^0 of a weak electrolyte cannot be determined experimentally. It can, however, be done with the help of Kohlrausch's law to be discussed later.

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