Teaching Precipitation Titration Methods: a Statistical Comparison of Mohr, Fajans, and Volhard Techniques

Abstract

Precipitation titrations are fundamental techniques in analytical chemistry, offering simplicity and generating a large data set in a short time. This laboratory experiment introduced students to three widely used titration methods: Mohr, Fajans, and Volhard. The study was conducted in two sessions, each lasting 100 min, and included both standard and real-world samples. In the first session, students quantified potassium iodide (KI) in solutions with varying concentrations, where the variables were related. Parametric statistical analysis was performed using repeated measures ANOVA (RMANOVA), while Friedman’s test was applied as its nonparametric counterpart for data not meeting normality or sphericity assumptions. In the second session, KI and sodium chloride (NaCl) were quantified in syrup and saline solutions, respectively, using statistical methods for independent groups. ANOVA was employed for parametric data, while the Kruskal–Wallis test served as its nonparametric equivalent. Results revealed that the Mohr method consistently produced higher concentration values compared to the Volhard and Fajans methods. This experiment provided students with practical experience in precipitation titrations, statistical analysis, and the use of open-source software for data interpretation, thereby enhancing their understanding of analytical chemistry and its real-world applications.