Introduction of Ionic equilibrium and Arrhenius Theory of Ionization for class XII Chemistry.

1. UNIT 3

2. Unit 3: Ionic Equilibrium.
Course Contents:
1. Introduction
2. Ionization of weak electrolyte (Ostwald dilution law)
3. Degree of ionization and ionization constant.
4. Strength of acids and bases in terms of Ka, Kb , pKa and pKb.
Values.
5. Acid – base concept.
6. i) Arrhenius concept ii) Bronsted Lowry concept iii) Lewis
concept.
7. Ionization of water , pH and pH scale.
8. Qualitative concept of hydrolysis of salt.
9. Solubility product principle and its applications
10. Common ion effect and its applications.
11. Application of solubility product principle in qualitative analysis.
12. Buffer solution.
13. (solving numerical problems based on solubility , solubility product
principle, pH and pOH )

3. Classification of Electrolytes:
 On the basis of whether substance can allow the passage of
electricity or not substances are classified as follows:
Electrolytes
Strong
electrolytes
Examples:
Strong acids, strong
bases and all salts.
Weak
electrolytes
Examples:
Weak acids, weak
bases.

4. Strong Electrolytes & Weak Electrolytes
Definition of strong electrolytes and weak electrolytes:
Strong
Electrolytes
• The electrolytes which are almost
completely ionized in solution are
called strong electrolytes. For example
NaCl, H2SO4, NaOH etc.
Weak
Electrolytes
• The electrolytes which do not ionize
completely in solution are called as
weak electrolytes. For example
CH3COOH, NH4OH, HCN, H3BO3,
ZnCl2 etc.

5. Introduction:
• Arrhenius Theory of Ionization:
• Swedish chemist, Svante Arrhenius in 1887 put forward a
successful theory to explain the process of ionization of an
electrolyte in solution. This is known as Arrhenius Theory of
ionization.
• Basic postulates of Arrhenius Theory of Ionization:
1. When an electrolyte is dissolved into water or polar solvents it
ionizes to form ions in the solution. These ions are free to move
throughout the bulk of the solution.
2. In any solution of an electrolyte, total number of positive
charges is equal to total number of negative charges.
3. The ions of an electrolyte in solution tend to recombine to form
unionized electrolyte. Thus, there exists a dynamic equilibrium
between ionized and unionized form of the electrolyte in
solution.

6. Introduction:
Such a dynamic equilibrium is described by a
constant known as ionization constant denoted by
K.For example when an electrolyte AB is
dissolved in water it ionizes as A+ and B- ions.
Then equilibrium is established.
AB + H2O ⇋ A+ + B-
The ionization constant is given by,
K=
𝐴+ 𝐵−
𝐴𝐵 𝐻2
𝑂
4. The properties of an electrolyte in solution are due
to the ions it gives into the solutions.

7. Introduction:
5. The fraction of total number of molecules split
into ions is known as degree of ionization
which denoted by alfa (α).
Mathematically,
𝐷𝑒𝑔𝑟𝑒𝑒 𝑜𝑓 𝑖𝑜𝑛𝑖𝑧𝑎𝑡𝑖𝑜𝑛(𝛼)
=
𝑁𝑜. 𝑜𝑓 𝑚𝑜𝑙𝑒𝑐𝑡𝑢𝑙𝑒𝑠 𝑠𝑝𝑙𝑖𝑡 𝑖𝑛𝑡𝑜 𝑖𝑜𝑛𝑠
𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠
It is commonly denoted by αc .

8. Factors affecting degree of ionization:
Nature of
electrolyte
Nature of
solvent
Dilution
Temperature
Presence of
common
ions