Answer: The molar mass of acid is 127.97 g/mol
Step-by-step explanation:
To calculate the number of moles for given molarity, we use the equation:

Molarity of NaOH solution = 0.270 M
Volume of solution = 36.4 mL
Putting values in above equation, we get:

The chemical equation for the reaction of NaOH and diprotic acid follows:

By Stoichiometry of the reaction:
2 moles of NaOH reacts with 1 mole of diprotic acid
So, moles of diprotic acid =

To calculate the number of moles, we use the equation:

Mass of acid = 0.629 g
Moles of acid = 0.004915 moles
Putting values in above equation, we get:

Hence, the molar mass of acid is 127.97 g/mol