Chalk Titration Lab
Description
This virtual lab simulates Experiment No. 5 from the CHM 1307 Analytical Chemistry manual: the determination of calcium carbonate (CaCO₃) content in a chalk sample using a back titration. Since CaCO₃ is insoluble and cannot be titrated directly, students dissolve a weighed chalk sample in a known excess of standardized hydrochloric acid, then back-titrate the unreacted acid with standardized sodium hydroxide using phenolphthalein as an indicator. Through fully interactive, drag-and-drop simulations of weighing, dissolving, diluting, pipetting, and titrating, students perform every step of the real wet-lab procedure themselves — including reading burette volumes, judging the color-change endpoint, and repeating titrations for concordant results — before working through the guided millimole-method calculation to determine the percentage purity of the chalk sample. The lab concludes with a short reflection and an interactive quiz that tests both conceptual understanding and calculation skills.
Learning Outcomes
By the end of this virtual lab, students should be able to explain the principle and purpose of a back titration and identify situations where it is preferred over direct titration; correctly execute and sequence the experimental steps of dissolving an insoluble solid in excess acid, performing a quantitative transfer and dilution, and carrying out an accurate acid–base titration with an appropriate indicator; apply stoichiometric relationships and the millimole method to calculate the amount of excess acid, the amount of acid consumed by the analyte, and the resulting mass and percentage purity of calcium carbonate in an unknown sample; interpret the phenolphthalein endpoint and understand the importance of concordant titration results for measurement precision; and critically evaluate sources of experimental error and relate calculated results to expected real-world values.