One student used 0.1 mol/L NaOH to titrate an unknown diprotic acid. The concentration of the unknown acid is 5.1 g/L, and the volume of the unknown acid is 15ml.
I. the volume of NaOH is 12.2 nL at the second equivalent point
II. pH at half of the first equivalent point is 3.09
III. pKa2 is 4.31
a. Calculate Ka1 and Ka2 of the unknown acid
b. Calculate the equivalent weight of the unknown acid
c. compare the Ka1, Ka2 and the equivalent weight of the unknown acid with the date in the table below, the name of the unknown acid can be identifed as:
Acid Ka1 Ka2 Equivalent Weight
Oxalic acid 5.4x10-2 5.1x10-5 63
phthalic acid 1.3x10-3 3.1 x 10-6 83
malic acid 9.0x10-4 2.5x10-5 67
citric acid 7.4 x 10-4 5.0x10-5 64