Question

What happens when an acid is added to a buffer?

Answer 1

1. A buffer is an aqueous solution consisting of different equivalents of acids and bases like a mixture of either a weak acid and its conjugate base or a weak base and its conjugate acid.
2. It resists the change in the pH values even if strong acid or base is added in a small quantity.
3. For example - A mixture of a weak acid Acetic acid (${\mathrm{CH}}_3\mathrm{COOH}$) and its salt Sodium Acetate (${\mathrm{CH}}_3\mathrm{COONa}$).
4. When a strong acid like hydronium ion(${\mathrm{H}}_3{\mathrm{O}}^{+}$) is added to the buffer solution it is consumed by a conjugate base (${\mathrm{A}}^{-}$) which gets converted into water and the weak acid of the conjugate base ($\mathrm{HA}$).
   ${\mathrm{A}}^{-}\left(\mathrm{aq}\right)+\hspace{0.17em}{\mathrm{H}}_3{\mathrm{O}}^{+}\left(\mathrm{aq}\right)\to {\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+\hspace{0.17em}\mathrm{HA}\left(\mathrm{aq}\right)$
5. This increases the amount of weak acid and decreases the amount of conjugate base present.
6. Thus, the pH of the buffer solution decreases by a very small amount which is much lesser than if the buffer system is not present.