Prelab Activity:

Titrations Continued – Titration of Household Products

1. A 2.40 g sample of vinegar was added to an Erlenmeyer flask along with 100 mL of deionized water and 3 drops of phenolphthalein indicator. It took 22.15 mL of 0.0981 M NaOH (aq) to reach the faint pink endpoint. The following balanced chemical equation represents the chemistry of the titration:

NaOH (aq) + CH₃COOH (aq) à CH₃COO^–Na⁺ (aq) + H₂O (l)

1. Calculate the mass % of acetic acid (CH₃COOH) in the vinegar sample.
2. Two subsequent trials found the mass % of acetic acid in vinegar to be 5.54% and 5.53%, respectively. Using the mass % found in part a, along with the values for subsequent trials, report an average value and standard deviation of mass % for the three trials. Report answer in the format: AVG ± S.D.

2.4.0 mL of 3.00 M HCl reacts completely with the CaCO₃ (active ingredient) in an antacid tablet. The remaining solution (excess HCl) is then titrated with 0.0981 M NaOH to the bromothymol blue endpoint.

1. Write the balanced chemical equation for the reaction of CaCO₃ (s) with HCl (aq).

2. If the volume of NaOH delivered at the endpoint is 22.20 mL, determine the amount (in milligrams) of CaCO₃ that was contained in the antacid tablet.