Final answer:
The concentration of the unknown acid HCl, when titrated with 0.500 M NaOH, is calculated to be 0.690 M using the equation M1V1 = M2V2 and the provided volumes of acid and base.
Step-by-step explanation:
To identify the molarity of an unknown acid using titration with a base such as NaOH, you can use the titration formula:
M1V1 = M2V2
where M1 is the molarity of the acid, V1 is the volume of the acid, M2 is the molarity of the base, and V2 is the volume of the base used at the equivalence point.
Given that 20.70 mL of 0.500 M NaOH is needed to neutralize 15.00 mL of HCl, we can find the molarity of HCl. The balanced chemical equation for the reaction is:
HCl + NaOH → NaCl + H₂O
The ratio of HCl to NaOH is 1:1, so we can rearrange the formula to solve for M1:
M1 = (M2V2) / V1
Substituting the known values:
M1 = (0.500 M × 20.70 mL) / 15.00 mL
M1 = (10.35 mmol) / 15.00 mL
M1 = 0.690 M
Thus, the molarity of the unknown HCl acid solution is 0.690 M.