1. What are the significant regions in the titration curve? Relate the characteristics of each region to the pH results obtained.
- There are four significant regions in each titration curve, namely the initial, pre-equivalence, equivalence, and post-equivalence points. These points are named according to its position relative to the equivalence point.
The equivalence point signifies the volume of titrant at which the solution becomes neutral. This is represented in the graph as the drastic change in pH, first with a sudden increase and a sudden decrease of pH.
At the initial point, no titrant has been added yet and the solution’s pH equates to the number of H+ ions originally present in the analyte.
At the pre-equivalence point, the titrant is now added. For this experiment, NaOH, a strong base, was added to KHP, a weak acid. With the addition of a strong base to a weak acid, a phenomenon similar to that of buffers occurs, and the solution initially resists drastic pH changes as backed up by the results of the experiment.
At the post-equivalence point, since the solution was already neutralized and excess NaOH is still added, the solution’s pH further increases.
2. Why is continuous stirring important in potentiometric titration?
- Continuous stirring allows for the formation of incremental hotspots, which allows for a higher concentration of the titrant in a localized area compared to the fluid around it. This allows for faster endpoints.
3. Why should the increments of addition be narrowed down as the titration approaches the equivalence point?
- Because as the titration nears the equivalence point, the changes in pH become larger, specifically at the equivalence point. The most drastic change happens at this point and the continuous addition of 1mL increments will not accurately show at which volume the equivalence point occurred at.
4. Why is potentiometry a suitable method in determining pKa of weak acids?