post-lab questions hat are two possible sources of error in the experiment? explain 2. when an acid reacts completely with a base the process is often called neutralization. if the product mixture is neutral, the ph should be 7 at the equivalence point. what is the ph at the equivalence point for the reaction in part i? if it is not equal to 7, explain why. 3. phosphoric acid has three ionizable hydrogens but only two equivalence points were observed. explain why the third equivalence point is not observed.

Here are the answers to the post-lab questions based on the gathered information:

1. Two possible sources of error in the experiment could be:
   • Inaccurate measurement of the volume of titrant added, which can happen due to limitations of the burette or human error in reading the volume (e.g., parallax error).
   • Contamination or improper cleaning of equipment, which affects solution concentrations and reaction outcomes.
2. The pH at the equivalence point depends on the strength of the acid and base involved. If a strong acid reacts with a strong base, the pH at the equivalence point is 7 (neutral). However, if the pH at the equivalence point in the reaction of part i is not 7, it could be because a weak acid or weak base is involved, changing the pH to either less than 7 (if strong acid and weak base) or greater than 7 (if strong base and weak acid).
3. Phosphoric acid has three ionizable hydrogens, but only two equivalence points may be observed because the third ionization produces a very weak acid (third dissociation constant is very low), making the third equivalence point difficult to detect during titration.

These explanations cover typical errors in titrations, the relationship between pH and neutralization in acid-base reactions, and why not all equivalence points of polyprotic acids may be observed.