Titration is a method used to react two substances by drop-wise addition until significant color change will occur in the analyte (solution being titrated) when an indicator is added. Its purpose is to know the concentration of the titrant (solution that is dropped into the analyte).
You must be able to classify these two terms that are always confused with: endpoint and equivalence point. Equivalence point is the point in titration when moles of acid is equal to the moles of base. With that being said, the analyte solution should only consist of the salt and water. The endpoint, on the other hand, is the observable change you see when a color change happens after a single drop of the titrant.
Looking at the titration curves, they have the same endpoint at 40 mL. This means that when 40 mL of titrant is added, you can see a color change for both set-ups at the same time. But the similarity only ends there. Focusing on curve A, the pH is initially very low (at ph 1). This means that the analyte is a strong acid. As the base titrant is added, it slowly increases in pH, as well. Halfway the steep curve (vertical line), the pH is at pH 7. This means that the solution is neutral. It can only mean that the titrant is a strong base. Thus, curve A is for a strong acid-strong base reaction.
For curve B, the pH also starts low, but not that low to be a strong acid. So, the analyte is a weak acid. As the base is added, the pH increases as well. Halfway the steep curve, the pH is at 9. This means that your solution contains a basic salt. Hence, the base must be a strong base. Thus, curve B is for a weak acid-strong base reaction.
