What is degree of ionization ?| physical chemistry.
DEGREE OF IONIZATION
An electrolyte, when dissolved in water, break up into two charged particles called ions. The posiuv charged ions are termed cations and negatively charged as anions
AB⇆ A⁺ + B⁻
NaCl ➝ Na⁺ + Cl⁻
K₂SO₄➝ 2K⁺ + SO₄²⁻
Electrolyte Ions
This process of splitting of the molecules into ions of an electrolyte is called ionization. The electrolyte may not be completely ionized. The ratio of number of molecules dissociated to the total qumber of molecules is known as degree of ionization or dissociation. It is denoted by π, i.e.
No of molecules dissociated into ions Degree of ionization (π) = ----------------------------------------
Total number of molecules
For strong electrolytes, π is almost equal to one as they almost completely ionize in aqueous solutions. The equation which involves the ionization of strong electrolytes is represented with single headed arrow directed to the right. For example,
HCI +H₂O ➝ H₃O⁺ + Cl⁻
But for weak electrolytes, π has very low value since they ionize to a very small extent. Degree of jonization increases with dilution and becomes maximum at infinite dilution. Complete ionization of the electrolyte does not occur. The ions formed in solution constantly reunite to form neutral molecules and thus, there is a state of dynamic equilibrium between the ions and the unionized molecules i.e.
AB ⇆ A⁺ + B⁻
On applying the law of mass action to the ionic equilibrium
[A⁺] [B⁻]
K=----------------
[AB]
where K is known as the dissociation or ionization constant.
The electrolytes having high value of K are known as strong electrolytes and those having low value of K as weak electrolytes.
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