A 50.0 mL sample of an unknown HCl solution was titrated with 0.449 M NaOH. To reach the equivalence point, 38.4 mL of the NaOH was used. What was the concentration of the HCl?

To find the concentration of the HCl solution, we calculate the moles of NaOH used at the equivalence point and use the stoichiometry of the reaction to determine the moles of HCl. We then divide the moles of HCl by the volume of the HCl solution to obtain its molarity, which is found to be 0.344712 M.

The concentration of the HCl solution can be calculated using a titration calculation. We start by finding out the number of moles of NaOH used to reach the equivalence point. To do this, we multiply the volume of NaOH used by its concentration:

Number of moles of NaOH = 0.0384 L imes 0.449 M = 0.0172356 moles

Since the reaction between HCl and NaOH is a 1:1 molar reaction (as shown by the equation HCl(aq) + NaOH(aq)
arr NaCl(aq) + H2O(l)), the number of moles of HCl will also be 0.0172356 moles. We then divide this number by the volume of HCl solution to find the molarity:

Molarity of HCl = 0.0172356 moles / 0.0500 L = 0.344712 M

Therefore, the concentration of the HCl solution is 0.344712 M.