Hello,
Can anyone help me with this question or point to where I could obtain an answer...
1. When performing diprotic acid titrations, you may see two clear endpoints or one may not be unclear.
a. When do the unclear endpoints occur?
Well, in the cases I examined, the second endpoint isn't visible is K
a2 is comparable with K
w, for example considering the third dissociation of H
3PO
4.
Another case happens if the two K
a aren't so different, as in the case of K
a1 and K
a2 of EDTA.
b. In which acids from the list below would you expect the endpoint to be unclear? Explain.
Acid FW pKa1 pKa2
Malonic acid 104.06 2.85 5.70
Maleic acid 116.07 1.92 6.23
Fumaric acid 116.07 3.02 4.38
Succinic acid 118.09 4.21 5.64
Itaconic acid 130.10 3.85 5.45
Glutaric acid 132.13 4.31 5.42
Thank you!
Given the rules I wrote before, I can assess that, for sure, Fumaric acid has only one endpoint:
http://www.demochem.de/chembox_diprotic_tit-e.htmAs an analogy, Succinic, Glutaric and Itaconic acid will have only one endpoint.
Probably, Malonic acid has two endpoints, even if they won't be so far.