Acidic Buffer solution

Definition:  Buffer solution is a solution which has the ability to maintain its pH when a small amount of strong acid or strong base is added.

  Two types of buffer solution

i)        Acidic Buffer – contains weak acid and its conjugate base (pH < 7)

ii)      Basic Buffer – contains weak base and its conjugate acid (pH > 7)

	Acidic Buffer Solution (Weak acid + conjugate base)
Preparation	By adding a weak acid to a salt which contains its conjugate base.
Example	CH3COOH  and  CH3COONa
Reaction	(W.A) : CH3COOH(aq)  + H2O(l)   CH3COO-(aq)  +   H3O +(aq) (C.B) :  CH3COONa(aq) →    CH3COO-(aq)   +   Na+(aq)
Henderson-Hasselbalch’s equation	pH = pKa  +  log  [ conjugate base ]                                 [ weak acid ] pH = - log Ka  +  log  [ conjugate base ]                                        [ weak acid ]
Addition of a small amount of strong acid	When a small amount of acid is added (H+), H+(aq) + CH3COO-(aq) → CH3COOH(aq) Acid (H+) form strong acid reacts with CH3COO- to form CH3COOH. Acid added is consumed. Concentration of [CH3COOH] increase, but concentrations of [CH3COO-] decrease. As a result, pH of the solution is not much affected.
Addition of a small amount of strong acid	When a small amount of base is added (OH-), OH-(aq) + CH3COOH (aq) →CH3COO- (aq) + H2O(l) Base (OH-) form strong base reacts with CH3COOH to form CH3COO-. Base added is consumed. Concentration of [CH3COO-] increase, but concentrations of [CH3COOH] decrease. As a result, pH of the solution is not much affected.
NOTE: The pH of a buffer solution can always be maintained no matter a strong acid or a strong base is added