A student completes a titration by adding 12.0 milimeters of NaOH (aq) of unknown concentration to 16.0 milimeters of 0.15 HCl (aq). What is the molar concentration of the NaOH (aq) ?

The balanced equation for the above reaction is as follows

NaOH + HCl - - - > NaCl + H₂O

stoichiometry of NaOH to HCl is 1:1

number of HCl moles reacted - 0.15 mol/L x 0.0160 L = 0.0024 mol

therefore number of NaOH moles reacted - 0.0024 mol

there are 0.0024 mol of NaOH in 12.0 mL

therefore in 1000 L - 0.0024 mol / 12.0 mL x 1000 mL = 0.20 mol

molarity of NaOH is 0.20 M