The resulting solution at the equivalence point will have a pH dependent on the acid and base’s relative strengths. You can estimate the equivalence point’s pH using the following rules:
- A strong acid will react with a weak base to form an acidic (pH < 7) solution.
- A strong acid will react with a strong base to form a neutral (pH = 7) solution.
- A weak acid will react with a strong base to form a basic (pH > 7) solution.
When a weak acid reacts with a weak base, the equivalence point solution will be basic if the base is stronger and acidic if the acid is stronger; if both are of equal strength, then the equivalence pH will be neutral. Weak acids are not often titrated against weak bases, however, because the color change is brief and therefore very difficult to observe.
You can determine the pH of a weak acid solution being titrated with a strong base solution at various points; these fall into four different categories: (1) initial pH; (2) pH before the equivalence point; (3) pH at the equivalence point; and (4) pH after the equivalence point.
Titration of a weak acid by a strong base: The pH of a weak acid solution being titrated with a strong base solution can be found at each indicated point.