Question

Imagine that you are the quality control analyst supervising the synthesis of aspirin, HC9H7O4, a monoprotic acid. One tablet is required to contain 325 mg of aspirin. To analyze your product, you dissolve one tablet in 230. ml H2O, then titrate this solution with a 0.1000 M NaOH. You find that 18.87 mL of NaOH solution are required to reach the endpoint. How many mg of aspirin are actually in the tested sample tablet?

Answer 1

Answer:

340.0mg of aspirin in the tested sample tablet

Explanation:

The titration of aspirin with NaOH obeys the following equation:

HC₉H₇O₄ + NaOH → C₉H₇O₄⁻ + Na⁺ + H₂O

As the complete titration spent 18.87 mL of 0.1000M NaOH, moles of NaOH are:

0.01887L × (0.1000mol / 1L) = 0.001887 moles of NaOH. As 1 mole of base reacts with 1 mole of aspirin, moles of aspirin are: 0.001887 moles of aspirin.

As molar mass of aspirin is:

C: 12.01g/mol × 9: 108.09g/mol

H: 1.01g/mol × 8: 8.08g/mol

O: 16g/mol ×4: 64g/mol

180.17g/mol. Mass of aspirin in the tested sample are:

0.001887 moles of aspirin × (180.17g / mol) = 0.3400g = 340.0mg of aspirin in the tested sample tablet