Question

1. How does the titration of a diprotic acid differ from a monoprotic acid (like HF)?

2. How does the titration of a weak base with a strong acid differ from weak acid-strong base titration. (Review pages 848 - 850.) Note: you could perform these titrations from the chemical cabinet in this lab.

3. What kind of pH (above 7, below 7, or 7) do you expect at the equivalence point from the titration of a weak acid with a strong base?

4. What kind of pH (above 7, below 7, or 7) do you expect at the equivalence point from the titration of a weak base with a strong acid?

5. In a real lab, the volume of the "drop" cannot be so easily controlled. Drops come in various sizes and the smaller the drop, the finer the titration. This is one of those "art" parts of laboratory work. Discuss how a real lab titration would differ from your on-line lab.

Answer 1

1. In case of monoprotic acid we would have only one equivalence point (pH > 7) as only one H is present. On the other hand in case of a diprotic acid we would have two equivalence points in the, first will have pH < 7 and the second would be pH > 7, since it has two H's in the acid. We would need 2 equivalents of base for neutralization of a diprotic acid as opposed to 1 equivalent base needed for a monoprotic acid.

2. For the titration of a weak acid with a strong base, at the equivalence point we would have an excess of OH- in the solution, making the pH > 7, basic. On the other hand in case of titration of weak base with strong acid, at equivalence point we would have an excess of H+ in solution, making the pH < 7, acidic.

3. The pH at the equivalence point would be above 7 in case of titration of weak acid and strong base.

4. The pH at the equivalence point would be below 7 in case of titration of weak base and strong acid.

5. In real life titration the equivalence point will slightly differ with each titration depending upon how fine and slow or fast addition of titrant is done. Whereas, in case of on-line lab the equivalence point will be sharp.