The COVID-19 pandemic posed a significant challenge for chemistry faculty across the country. As school systems moved from traditional to online learning, faculty were faced with the daunting task of converting chemistry labs from the traditional “wet-lab” setting to an online virtual format. A viable alternative to virtual labs is home-based chemistry experiments. The purpose of this paper is to describe a viable, low-cost, and safe alternative for the quantitative analysis of ascorbic acid in juiced fruits and vegetables. We describe a modified version of the iodine-ascorbic acid redox reaction. The lab is designed as a “home-based” lab using only three household chemicals: namely 2% iodine tincture (CVS® brand), food-grade ascorbic acid, and corn starch. In addition, this procedure circumvents the tedious preparation of iodine solutions by using store-bought iodine and plastic cups instead of glass beakers. Ascorbic acid is used to standardize the iodine solution and the titrations are done using two methods: the burette method and the drop-wise method. Four different concentrations of ascorbic acid were prepared and titrated with iodine. Graphs of ascorbic acid concentration versus the volume of iodine used to reach the equivalence points (for burette and drop-wise methods) yielded linear equations which were used to determine the ascorbic acid concentrations in juiced samples. The linear equations were y = 3.389x + 0.0735 (R2 = 0.997) for the burette and y = 25.786x + 0.5797 (R2 = 0.99) for the drop-wise method. Ascorbic acid solutions and juice samples were prepared on the same day. Twenty-seven different fruits and vegetables were purchased (grocery store), juiced (electric juice extractor), and titrated with 0.04% iodine solution. Using the linear equations, we determined that the mean ascorbic acid concentration (mg/mL, n = 3) ranged from 1.86 ± 0.08 mg/mL for sweet red peppers to as low as 0.11 ± 0.02 mg/mL for an apple. The procedure we describe is fast, accurate, easy, and suitable for home-based chemistry labs.

Quantitative analysis of vitamin C in 27 fruits and vegetables: A cost-effective home-based chemistry lab

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.