Question

The flask shown here contains 0.865 g of acid and a few drops of phenolphthalein indicator...

The flask shown here contains 0.865 g of acid and a few drops of phenolphthalein indicator dissolved in water. The buret contains 0.240 M NaOH.

What volume of base is needed to reach the end point of the titration?

What is the molar mass of the acid (assuming it is diprotic and that the end point corresponds to the second equivalence point)?

The volume needed is 12.0mL.

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Answer #1

H2A   + 2 NaOH ---------------------> Na2A + 2H2O

moles of H2A = 2 x moles of NaOH

                        = 2 x 0.240 x 12 x 10^-3

                        = 0.00576

moles = mass / molar mass

0.00576 = 0.865 / molar mass

molar mass of acid = 150.17 g /mol

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