Can a buffer resist \(\mathrm{pH}\) changes for any added amount of strong acid or base? Explain.

A buffer is a mixture of weak acid and its conjugate base or a weak base and its conjugate acid. It resists changes in pH when small amounts of strong acid or base are added. This ability comes from the equilibrium between the weak acid (or base) and its conjugate species. For example, let's consider an acidic buffer composed of a weak acid, HA, and its conjugate base, A-: \[HA \rightleftharpoons H^+ + A^-\] When a strong acid (HX) is added to the solution, it donates protons (H+) to the conjugate base (A-): \[HX + A^- → HA + X^-\] Since A- acts as a proton acceptor, the increase in H+ concentration, and thus pH change, is minimized. Similarly, when a strong base (MOH) is added to the solution, the weak acid (HA) donates protons (H+) to the hydroxide ions (OH-), forming water (H2O) and the conjugate base (A-): \[MOH + HA → MA + H_2O\] In this case, the weak acid acts as a proton donor, decreasing the effect of added OH- on pH change.

Buffer capacity refers to the amount of strong acid or base that can be added to a buffer solution without causing a significant pH change. Buffers have maximum capacity when the concentrations of their buffer components (weak acid or base and respective conjugate species) are high and equimolar. However, there is a limit to the buffer's resistance to pH changes. If a very large amount of strong acid or base is added, the equilibrium will be significantly disrupted, and the buffer will lose its ability to resist further pH changes. The exact amount of strong acid or base that can be successfully neutralized by a buffer depends on the ratio of the weak acid/base to its conjugate and the magnitude of their concentrations.

A buffer can resist pH changes when small amounts of strong acid or base are added, thanks to the equilibrium between the weak acid/base and its conjugate species. However, there is a limit to the buffer's capacity to maintain pH stability. When a large amount of strong acid or base is added, the buffer components become overwhelmed, and the buffer loses its ability to resist further pH changes. Therefore, it cannot resist pH changes for any added amount of strong acid or base.