Potentiometric determination of ions with ion selective electrodes and determination of water hardness by complexometric titration are two laboratory practices commonly offered in analytical chemistry laboratories. The former covers fundamentals of electrochemistry and the latter offers basic concepts involving in titration such as equivalence point versus end point, and visual indicators. This work is undertaken to develop an experiment for determination of calcium in various natural water samples. The calcium determination is accomplished through complexometric titration with newly acquired automatic titrators. The calcium concentrations are determined potentiometrically using a calcium ion selective electrode. The experiment provides a comparison of two classic laboratory practices by combining their learning objectives and adding an in-field component with snow and Rouge River sampling. The addition of the in-field component provides students an opportunity to link the concepts learned in the lecture to real-world sample analysis. The preliminary results show that the calibration curve covers a concentration range of 5.0 x 10-3 to 2.0 x 10-5 M calcium ions with a linear regression coefficient of 0.996. The method has been successfully used to determine the concentrations of calcium ions in tap water, snow, and river water samples. The comparison activities between the two techniques can potentially lead to greater learning gains than traditional instruction.

Determination of calcium with automatic potentiometric and complexometric titrations using a calcium ion selective electrode

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