The solution which resist the change in pH on deletion or with the addition of small amount of acid or Alkali are called Buffer Solution.
Example
$CH_3COOH + CH_3COONa$
$H_2CO_3 + HCl $
Types of Buffer Solutions
There are two primary types of Buffer solutions
Acidic Buffer
Weak acid and its salt with strong base forms acetic buffer. The pH of solution is less than 7.
Example
$H_2CO_3 + HCl$
$CH_3 COOH + CH_3COONA$
Basic Buffer
Weak base and its salt with strong acid forms basic buffer. pH greater than 7.
Example
$NH_4 Cl + NH_4OH$
Handerson-Hasselbalch Equation
This equation can be use to prepare the Acidic and Basic solutions Acidic Buffer
$\text {pH of acid buffer} = pK_a + log \frac {[salt]}{[acid]}$ Basic Buffer
$\text {pH of bassic buffer} = pK_a + log \frac {[salt]}{[base]}$
How Buffers solution works
Lets understand by taking the example of
$CH_3COOH + CH_3COONa \rightleftharpoons CH_3COO^- + H^+ + Na$
When strong acids are added, the H+ ions combine with the CH3COO– ions to give a weakly ionized acetic acid.So equilibrium Shift to the Acetic acid side
When strong base substances are introduced to this buffer solution, the hydroxide ions react with the acids which are free in the solution to form water, So equilibrium Shift to the Acetic ion side
$CH_3COOH + OH^– \rightleftharpoons CH3COO^– + H_2O$
