To determine the concentration of a hydrochloric acid HCl solution using sodium hydroxide NaOH as the titrant, you can perform an acid-base titration. In this process, a solution of known concentration NaOH is used to react with a solution of unknown concentration HCl until the reaction is complete. The point at which the reaction is complete is called the equivalence point. The balanced chemical equation for the reaction is:HCl aq + NaOH aq NaCl aq + H2O l Since the stoichiometry of the reaction is 1:1, the moles of HCl are equal to the moles of NaOH at the equivalence point. You can use the formula:moles = molarity volumeTo find the volume of the 0.2 M NaOH solution needed to neutralize 25 mL of 0.1 M HCl solution, first, determine the moles of HCl:moles of HCl = molarity volumemoles of HCl = 0.1 M 0.025 L convert 25 mL to liters by dividing by 1000 moles of HCl = 0.0025 molSince the stoichiometry of the reaction is 1:1, the moles of NaOH needed are also 0.0025 mol. Now, use the moles of NaOH and the molarity of the NaOH solution to find the volume:volume of NaOH = moles / molarityvolume of NaOH = 0.0025 mol / 0.2 Mvolume of NaOH = 0.0125 LConvert the volume to milliliters:volume of NaOH = 0.0125 L 1000volume of NaOH = 12.5 mLSo, 12.5 mL of 0.2 M NaOH solution is needed to neutralize 25 mL of 0.1 M HCl solution.