10. A weak acid with an initial pH of 3.2 was titrated with a strong base. 15 mL of 0.1 M NaOH was added to the acid to reach the equivalence point at a pH of 8.6. What would you expect the approximate pH of the analyte to be after the first 5 mL of 0.1 M NaOH was added?
8.6
3.4
5.1
7.2
I would choose 5.1. If one third of the base is added (in which the whole 15ml was utilized to bring to a basic state of 8.6), it must be 5.1, as the other answers are mathematically impossible.
To determine the approximate pH of the analyte after the first 5 mL of 0.1 M NaOH was added, we need to consider the chemical reaction taking place during the titration.
In this case, a weak acid (analyte) is being titrated with a strong base (NaOH). The initial pH of the weak acid is 3.2, and the equivalence point is reached when 15 mL of 0.1 M NaOH is added and the pH is 8.6.
During the titration of a weak acid with a strong base, the pH will gradually increase as more base is added. However, the rate at which the pH changes depends on the relative concentrations of the analyte and titrant.
In the given scenario, after 15 mL of NaOH is added, the pH reaches 8.6, indicating that the reaction is approaching the equivalence point. Since the pH is increasing and getting closer to neutral (pH 7), it suggests that the weak acid is being neutralized by the added base.
Therefore, if we consider the first 5 mL of NaOH that was added and assume that the pH change is roughly proportional to the amount of base added, we can estimate that the pH of the analyte after the first 5 mL of NaOH would be closer to the initial pH of the weak acid, which is 3.2.
So, the approximate pH of the analyte after the first 5 mL of NaOH was added would be around 3.2.
Therefore, the correct answer is 3.4.