What causes unclear endpoints in diprotic acid titrations?

In summary, when performing diprotic acid titrations, there may be two clear endpoints or one may be unclear. The unclear endpoints occur when the separation of pKa values is too close. This can be seen in acids such as malonic acid, maleic acid, fumaric acid, succinic acid, itaconic acid, and glutaric acid, where the pKa values are close to each other.
  • #1
Nana00
3
0
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!
 
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  • #2

1. What is a diprotic titration curve?

A diprotic titration curve is a graph that shows the changes in pH as a strong acid is added to a solution containing a weak diprotic acid. It is used to determine the equivalence point and the dissociation constants of the weak acid.

2. How is a diprotic titration curve different from a monoprotic titration curve?

A diprotic titration curve involves the addition of a strong acid to a solution containing a weak diprotic acid, while a monoprotic titration curve involves the addition of a strong acid to a solution containing a weak monoprotic acid. This means that a diprotic titration curve will have two equivalence points, while a monoprotic titration curve will only have one.

3. What is the significance of the first and second equivalence points on a diprotic titration curve?

The first equivalence point represents the point at which the amount of added strong acid is equal to the amount of the first proton that has been dissociated from the weak acid. The second equivalence point represents the point at which the amount of added strong acid is equal to the amount of the second proton that has been dissociated from the weak acid.

4. How do you calculate the dissociation constants from a diprotic titration curve?

The dissociation constants, Ka1 and Ka2, can be calculated by using the Henderson-Hasselbalch equation at the first and second equivalence points. These values can then be used to determine the acid dissociation constants of the weak diprotic acid.

5. What factors can affect the shape of a diprotic titration curve?

The shape of a diprotic titration curve can be affected by the concentration of the weak diprotic acid, the strength of the strong acid being added, and the presence of any other substances in the solution that may react with the acids. Additionally, the values of the dissociation constants can also impact the shape of the curve.

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