Statistical Comparison of Results of Redox Titrations Using K-2 CR-2O-7 and KIO-3 in the Undergraduate Analytical Chemistry Lab

Reducing the quantity of hazardous substances used and hazardous waste generated by under- graduate laboratory experiments is important. However, simply replacing hazardous compounds with less hazardous reagents may not retain the pedagogical (or analytical) goal of the experiment if the chemistry does not fundamentally work. We evaluated several literature-based replacement oxidants for K2Cr2O7 (potassium dichromate) and identified KIO3 (potassium iodate) as the only che- mically viable alternative for thiosulfate standardizations, consistent with use of iodate by others. Using ANOVA analysis, two years of student results where K2Cr2O7 was used as the oxidant were compared with two years of student results where KIO3 was used as the oxidant (ANOVA -value for precision = 0.684; ANOVA -value for accuracy = 0.638). This comparison of multiple years of student data enabled us to confidently eliminate toxic Cr(VI) from a quantitative iodometric titration in our second year analytical chemistry laboratory, while students maintained a high level of both accuracy and precision.