Conductance for CBCS, students of B.Sc

1. Notebook: Physical Chemistry 3rd sem
Created: 28-08-2020 21:40 Updated: 29-08-2020 10:35
Author: Ankit Srivastava
Conductance Unit-3
Conductivity,equivalent and molar conductivity and their variation with dilution for weak and
strong electrolytes, Kohlrausch Law of independent migration of ions, Transference number and
its experimental determination using Hittorf and moving boundary methods, Ionic mobility,
Applications of conductance measurements: determination of degree of ionization of weak
electrolytes,Solubility and solubility products of sparingly soluble salts, ionic product of water,
hydrolysis constant of a salt. Conductometric titrations (only acid-base).
Conductivity
Equivalent Conductivity

2. Molar Conductivity
Variation of Conductivity and Molar Conductivity with
Dilution

3. Kohlrausch Law
Transport Number and its Experimental Determination

4. Hittorf’s Method for the Determination of Transport Number of Ions
On passing the current through a solution, concentration changes occur in the vicinity of the
electrodes. These changes are due to two factors.
1. Electrode Reactions
2. Migration Effects
In order to understand the nature of the changes caused by the above two factors near the
vicinity of electrodes, we consider the following two cases.

6. The Moving Boundary Method
In this method, the motion of ions under the influence of an applied potential is observed
directly.

8. Ionic Mobility
The ionic mobility (μ) is defined as the velocity attained by an ion moving through a gas under
unit electric field.
Applications of Conductance Measurement;
1. Determination of Degree of Ionization of Weak Electrolytes

9. 2. Solubility and solubility products of sparingly soluble salts
3. Ionic Product of Water

10. Hydrolysis Constant of Salt

11. Condumetric Titrations
The principle of conductometric titrations is based on the fact that during the titration, one of
the ions is replaced by the other and invariably these two ions differ in the ionic conductivity with
the result that the conductivity of the solution varies during the course of the titration.
Example, Titration of a Strong Acid with a Strong Base
HCl vs NaOH
Before addition of NaOH, the solution is having faster moving H+ ions but when NaOH is added
H+ is replaced with Na+ which is slower than H+ and as a result of which conductivity decreases.
But with the successive addition of NaOH the conc. of OH- ions increases which again is a fast
moving ion and hence conductivity again starts increasing.