Question

What is the molarity of 125ml of hydrochloric acid (HCl) needed to neutralize 5 Liters (5L) of 10M sodium hydroxide?

Answer 1

HCl + NaOH ==> NaCl + H2O

mols NaOH = molarity x liters = M x L = 10 M x 5 L = 50 moles.
From the equation 1 mol HCl neutralizes 1 mol NaOH; therefore, you need 50 mols HCl. For HCl moles = M x L. You know L = 0.125 and moles = 50. Solve for M.