NCEA Level 3 Chemistry – Aqueous Chemistry (AS91393) Practice Exam

The selection of the final pH is justified as it reflects the pH after the equivalence point on a titration curve. At the equivalence point, the amounts of acid and base have completely reacted, resulting in a solution that contains the salt and, depending on the nature of the acid and base used in the titration, possibly excess acid or base.

As the titration continues past this point, the pH will continue to change based on the nature of the excess reactant present. For example, if a strong base is in excess, the final pH will be quite high, indicating a basic solution; if a strong acid is in excess, the final pH will be low, indicating an acidic solution.

This final pH value shows the outcome of the titration once all the acid-base reactions have concluded and leftover reagents are influencing the solution's pH. Thus, it is a direct reflection of the solution composition after surpassing the equivalence point and represents the final state of the titration.