Final answer:
In a titration of a weak acid with a strong base, the pH gradually increases as the strong base is added and reacts with the weak acid to consume H+ ions. The pH rise becomes more rapid as the equivalence point approaches, and the pH is greater than 7 at equivalence due to the excess of conjugate base.
Step-by-step explanation:
Titration of a Weak Acid with a Strong Base
During the titration of a weak acid with a strong base, the solution experiences a gradual increase in pH before reaching the pre-equivalence point. As the strong base is added, it reacts with the weak acid to form water and the conjugate base of the weak acid. This process consumes protons (H+), which decreases the concentration of H+ ions and thus increases the pH of the solution. Not all of the weak acid dissociates, meaning the pH of a weak acid solution is greater than that of a strong acid at the same concentration. As the titration progresses and approaches the equivalence point, most of the H+ ions have been consumed, leading to a more rapid rise in pH.
Before the equivalence point is reached, the solution consists of the unreacted weak acid and its reaction product, the conjugate base. The pH reflects the balance between these species. The pH at the equivalence point is greater than 7, reflecting the fact that the conjugate base of the weak acid is now in excess and that it can further ionize to a certain degree.
For a weak acid-strong base titration, the titration curve will show a gradual increase in pH as base is added, a sharp rise near the equivalence point, and then a leveling off as more base is added past the equivalence point. The pH change is more gradual around the equivalence point compared to a strong acid-strong base titration because of the buffering capacity of the weak acid and its conjugate base.