Amperometric Method to Determine the Active Ingredients in Household Products: A Set of Undergraduate Laboratory Titration Experiments

Students enrolled in chemistry laboratories are often required to perform an experiment in which the amount of a specific ingredient in a household product is determined. A set of four amperometric titration experiments for the determination of iron in dietary supplement tablets, permanganate in a pond cleaner liquid, iodine in skin disinfectant liquid, and ascorbic acid in dietary supplement powder is presented. In each titration, a reagent or an analyte was added from the buret to the desired solution, and a small DC voltage was applied to two identical platinum electrodes placed in this solution. The current was monitored as a function of the added volume. The end point of each titration was monitored by the change in the current profile. The quantities (69 mg of iron per tablet, 0.29 M permanganate concentration in the pond cleaner, 1.0% w/v iodine in the skin disinfectant liquid, and 1009 mg of ascorbic acid per packet of dietary supplement powder) determined by the amperometric titrations agreed with those available on the manufacturer’s label. With the exception of one trial, the percent error values were less than 10%. The end point of the titration of each analyte determined by amperometry matched with the end point determined by the visual color change of the indicators. The experiments were aimed at the pedagogical learning objectives of plotting the current vs the reagent volume, applying stoichiometric mole relations to quantify the active ingredients in the household product, and comparing the quantity of the active ingredient with the manufacturer’s label. Students’ success in determining the quantities of active ingredients from multiple trials of the experiments aligned with the learning objectives. The results of the post-laboratory exercise indicated that the students met the learning objective of applying the stoichiometric mole relations. Third- and fourth-year undergraduate students performed the amperometric titrations as a laboratory experiment.