Review this equation: HCl + NaOH NaCl + H2O. What volume of a 6.0 M HCl solution is required to completely neutralize 125.0 ml of a 2.5 M NaOH solution?

Moles of NaOH = 125 ml * 2.5mol/L = 312.5 m moles

the same number of moles, of HCl must be the same but notice we have not given the volume, but the molarity, so the moles must be 312.5 m mole

so M. V = 312.5

6V = 312.5

V = 52.08 ml