Unknown Acid?

Question

A 6.50-g sample of an acid, HX, requires 137.5 mL of a 0.750 M NaOH solution for complete reaction. Calculate the molar mass of the acid.

A. 15.9 g/mol
B. 36.3 g/mol
C. 63.0 g/mol
D. 103 g/mol

Answer 1

so you know the volume and molarity of base used. so you can know the number of moles of base used.
NaOH ---> Na+ + OH-
OH- + H+ -----> H2O

from those reactions you know that the number of moles of base is equal to the number of moles H+

assuming it dissociated completely ie HX --> H + X you know how many moles of acid you have.

dividing the mass by the number of moles nets you the molar mass