Final answer:
To lower the pH of a buffer, adding a strong acid is the appropriate action. The strong acid would react with the conjugate base component of the buffer, which helps to maintain the pH at a relatively stable level despite the addition of the acid.
Step-by-step explanation:
To lower the pH of a buffer, you should add a strong acid. When a strong acid is added to a buffer solution, it reacts with the conjugate base present in the buffer. This reaction minimizes the increase in the hydrogen ion concentration and thus limits the change in pH.
Buffers are designed to maintain a stable pH when small quantities of acids or bases are added. A buffer typically contains a weak acid and its conjugate base in similar concentrations. For instance, a solution of acetic acid and sodium acetate forms an effective buffer. Adding strong bases to such a buffer results in the hydroxide ions reacting to form water, while adding strong acids will shift the equilibrium slightly, as shown in the equation BH+(aq) + H2O(l) ← B(aq) + H3O+(aq). The presence of these components allows the buffer to 'absorb' excess H+ ions from the added strong acid, thereby preventing significant changes in pH.