A Laboratory Module for Physical Chemistry and Analytical Chemistry: The Kinetics of Aspirin Hydrolysis and Its Quantitation in Pharmaceutical Tablets

Abstract

In this three-component laboratory module, upper-division chemistry students were introduced to the kinetics of the aspirin hydrolysis reaction and determined the concentration of its active pharmaceutical ingredient (acetylsalicylic acid-ASA) using a modern, benchtop ultraviolet–visible (UV–vis) absorption spectrophotometer. In the first component, students prepared analyte solutions from over-the-counter aspirin tablets and a relevant number of standards (n = 9–10) through both serial and parallel dilutions. In the second component, the ASA concentrations of three over-the-counter formulations (325 mg per tablet) were determined with percent differences as small as 1.1% using the Beer–Lambert law and external calibration curves. In the third component, students evaluated the reaction order (pseudo-first order), the rate constant (e.g., k = 3.0 × 10^–4 s^–1 at 75 °C), and the activation energy (E_a ∼ 67.3 kJ mol^–1) of the hydrolysis reaction of ASA at various temperatures (e.g., 25, 37, 50, 75, and 85 °C). The last component was completed using a student-centered instructional approach, namely, process-oriented guided-inquiry learning (POGIL), which helped refine students’ research process skills and both basic and in-depth laboratory skills (weighing, solution handling, micropipetting, operation of a pH meter and a modern, benchtop absorption spectrophotometer). The student and instructor evaluations indicated a positive learning experience and high interest in this laboratory that was inspired by the quality control and quality assurance of pharmaceutical drugs.