The graph above displays data for 12.00 mL of an unknown diprotic acid titrated

Question

The graph above displays data for 12.00 mL of an unknown diprotic acid titrated with 0.100 M KOH. What is the volume of titrant added at the following points according to the graph? (1) Based on the plot of the titration above, what is pKal of the diprotic acid? _ (1) Based on the plot of the titration above, what is pKa2 of the diprotic acid? _ (5) What is the volume of titrant added at the following points according to the plot in # 1. The first equivalence point: _ mL of KOH added The second equivalence point: _ mL of KOH added The point at which the pH = pKal of the analyte: _ mL of KOH added The point at which the pH = pKa2 of the analyte: _ mL of KOH added The point at which the pH = (pKal + pKa2)/2: _ mL of KOH added

Explanation / Answer

For Q1, please add the moles of H2A present....

Q2.

pKa1 --> must be in first half equivalence point (volume)

V for 1st point --> 10 mL, therefore V 1/2 = 5 mL; the pH at this V, pH = 3; that is pKa = 3

pKa2 --> must be in second half equivalence point (volume)

V for 2nt point --> 20mL, therefore V 1/2 = 15 mL; the pH at this V, pH = 7; that is pKa = 7

Q4.

a) first equivalence point --> 10 mL ( when pH changes drastically)

b) second equivalence point --> 20 mL ( when pH changes drastically)

c) when pH = pKa1 ---> 3; will be then 5 mL

d) when pH = pKa2 ---> 7; will be then 15 mL

e) point in which pH = (pKa1+pK2)/2 = 5 ... 10 mL

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