Here is the information for each post-lab question:
- Two possible sources of error in the experiment could be:
- Inaccurate measurement of the volume of titrant added, due to parallax error or air bubbles in the burette.
- Contamination or improper cleaning of the glassware affecting solution concentrations.
- The pH at the equivalence point depends on the acid-base strength:
- For a strong acid-strong base reaction, the equivalence point pH is 7 (neutral).
- If the pH is not 7, it is likely because the acid or base is weak, which leaves either acidic or basic species in solution, causing the pH to shift.
- For phosphoric acid with three ionizable hydrogens but only two equivalence points observed:
- The third equivalence point may not be observed because the third hydrogen ion is very weakly acidic.
- This means the third ionization occurs at a much higher pH and is less pronounced, often blending with the second equivalence point or being too weak to detect distinctly.
This summarizes the likely answers based on typical titration and acid-base chemistry principles.