What causes unclear endpoints in diprotic acid titrations?

[Nana00]

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 be unclear.
a. When do the unclear endpoints occur?
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!

 

[Borek]

It depends on the separation of pKa values, if they are too close, there will be no separation of endpoints. See acid base titration - polyprotics and mixtures.