Best Answer: Because the equation is this: MaVa = MbVb
Ma = Molarity of H+ ions
Va = Volume of acid solution in mL
Mb = Molarity of OH- ions
Vb = Volume of base solution in mL
Since H2SO4 is a diprotic base (two hydrogens), then one mol of H2SO4 will disassociate into two H+ ions
Therefore in the equation you must double the molarity of H2SO4, because the formula doesn't ask for the molarity of the acid, it asks for the molarity of H+ ions.
Therefore:
Ma×Va = Mb×Vb
(0.5 M)× Va = (0.25 mL)×(1.5M)
Va = Mb×Vb / Ma
Va = 0.75 mL
