4. A 10.0 mL sample of unknown HCl (aq) is transferred to an Erlenmeyer flask along with 90 mL of deionized water and 3 drops of phenolphthalein indicator. The solution is titrated to the faint pink endpoint with 15.20 mL of the same NaOH (aq) solution used in problem 3. Calculate the concentration of HCl (aq) in the original 10.0 mL sample.
