Explain how a buffer solution resists the pH change when an acid or alkali is added.

HA <----> H+ + OH-Acid:Adding an acid increases the concentration of H+ ions as acids are proton donors. These H+ ions react with the conjugate base, A-, to form HA and thus shift the equilibrium position to the left to reduce the concentration of H+.Base:Adding a base increases the concentration of OH- ions. These react with the H+ ions already in solution to form H2O. This reduces the concentration of H+ and so the equilibrium position shifts right to reduce the change due to Le Chatelier's principle.