Question

I am looking for the molecular weight of an unknown acid in a titration.

My acid is diprotic, the equivalence points are at 1.4 mL (of NaOH added) and 3 mL (of NaOH added).

The molarity of NaOH is 0.98 M. I used 0.025 g of the unknown acid in the titration.

How do I find the molecular weight of the unknown acid?

Answer 1

H2A + NaOH ------> NaHA + H2O

moles of NaOH = M*Volume

                           = 0.98*(1.4/1000)

                           = 0.001372

then moles of acid at first equivalence point = 0.001372

moles = mass/molarmass

molarmass = mass/moles = 0.025/0.001372 = 18.2 g