Chemistry - Ionic Equilibrium Question with Solution | TestHub

If small amount of an acid or alkali is added to a buffer solution, it converts them into unionised acid or base. Thus, its $\mathrm{pH}$ remains unaffected or in other words its acidity/alkalinity remains constant. e.g., $$\begin{array}{rl}& {\mathrm{H}}_3{\mathrm{O}}^{+}+A^{-}\rightleftharpoons {\mathrm{H}}_2\mathrm{O}+\mathrm{H}A\\ & {}^{-}\mathrm{OH}+\mathrm{H}A⟶{\mathrm{H}}_2\mathrm{O}+A^{-}\end{array}$$ If acid is added, it reacts with $A^{-}$to form undissociated HA. Similarly, if base/alkali is added, ${\mathrm{OH}}^{-}$combines with $\mathrm{H}A$ to give ${\mathrm{H}}_2\mathrm{O}$ and $A^{-}$and thus, maintains the acidity/ alkalinity of buffer solution.