BASIC BUFFER SOLUTION

	Basic Buffer Solution (Weak base + conjugate acid)
Preparation	By adding a weak base to a salt which contains its conjugate acid.
Example	NH3 and NH4Cl
Reaction	(W.B) : NH3 + H2O   NH4+   + OH- (C.A):  NH4Cl  → NH4+  + Cl-
Henderson-Hasselbalch’s equation	pH = - log Kb  +  log  [ conjugate acid ]                                     [ weak base ]
Addition of a small amount of strong acid	When a small amount of acid is added (H+), NH3(aq) +  H+(aq) →NH4+(aq) Acid (H+) form strong acid reacts with NH3to form NH4+. Acid added is consumed. Concentration of [NH4+] increase, but concentrations of [NH3] 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) + NH4+ (aq) →NH3 (aq) + H2O(l) Base (OH-) form strong base reacts with NH4+ to form NH3 Base added is consumed. Concentration of [NH3] increase, but concentrations of [NH4+] 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