The reaction of Ca(oH)2 with HCl produces calcium chloride (CaCl2) and water (H2O). The stiochiometric equation is 2HCl + Ca(OH)2 = CaCl2 + 2H2O. In this case, 2 moles of HCl stoichiometrically reacts with one mole of calcium hydroxide. Hence for 3.5 moles of Ca(OH)2, there should be 1.75 moles of HCl needed. Given 0.85 M HCl, to get the volume, we divide 1.75 moles by 0.85 M. The volume needed is 2.0588 liters.
