Final answer:
In titrating a weak monoprotic acid with NaOH, the equivalence point pH will be above 7, and the choice of acid-base indicator should reflect this. The buffering action of the conjugate base affects the pH change during the titration, especially near the equivalence point.
Step-by-step explanation:
When titrating a weak monoprotic acid such as acetic acid with a strong base like NaOH at 25°C, several considerations must be taken into account. The pH changes occurring during the titration are different from those in the titration of a strong acid with a strong base, since the conjugate base of the weak acid has a buffering effect. Notably, the equivalence point pH will be greater than 7, because the conjugate base of the weak acid reacts with water in a hydrolysis reaction, raising the pH of the solution.
Throughout the titration process, especially near the equivalence point, the pH of the solution will increase more rapidly as the neutralization reaction nears completion and most of the H+ ions have been consumed. In the case of acetic acid and NaOH, the equivalence point pH is around 8.72. It is essential to choose an appropriate acid-base indicator that changes color around this pH to accurately determine when the titration has reached the equivalence point.