student titrated 15.00 mL of HCl of an unknown concentration with a solution of 0.0670 M NaOH. This titration used 19.06 mL of the 0.0670 M NaOH to reach the end point. Determine the concentration of the unknown HCl in one set up. You may look at the steps used in the previous problem to recall what fractions need to be in the set-up to solve this problem. 1. Fill in the fractions required to determine the concentration of HCl.