Explain the action of acidic buffer.

Explanation

Consider an acidic buffer of `CH_(3)COOH` and `CH_(3)COONa`. In aqueous solution of acidic buffer, the following equilibrium exists :
`CH_(3)COOH hArr CH_(3)COO^(-)(aq) + H^(+)(aq)`
`CH_(3)COONa hArr CH_(3)COO^(-)(aq) + Na^(+)(aq)`
Suppose we add small amount of HCl to it, the `H^(+)` ion from acid combine with `CH_(3)COO^(-)` of buffer and reacts as follows :
`CH_(3)COO^(-)(aq) + H^(+)(aq) hArr underset("weakly ionised")(CH_(3)COOH)`
As `H^(+)` ions from acid are being neutralised by `CH_(3)COO^(-)` of buffer, the pH of buffer does not change.
Suppose we add small amount of NaOH to it, the `OH^(-)` ions from base will combine with `H^(+)` ions of water.
`H^(+)(aq) + OH^(-)(aq) rarr underset("weakly ionised")(H_(2)O)`
Therefore, there is no change in pH of buffer solution.