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

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.