In the Laboratory
A Simple Computer-Interfaced Calorimeter: Application to the Determination of the Heat of Formation of Magnesium Oxide
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Sze-Shun Wong, Natasha D. Popovich, and Shelley J. Coldiron* Department of Chemistry, Iowa State University, Ames, IA 50011; *
[email protected] Despite the importance of operational amplifiers in chemical instrumentation, laboratory experiments based on their use are not often found in the literature or incorporated into the instrumental analysis curriculum. Since chemists are often called upon to not only operate but also troubleshoot and even construct the instruments they use, the basic knowledge of building electrical circuits with operational amplifiers is beneficial in both academic and industrial professions. In this paper, we present an experiment that can be used to demonstrate applications of operational amplifiers in chemical measurement and control systems and in interfacing experiments to computers, as well as to teach the basics of thermochemistry. We believe that this experiment is best suited for an instrumental analysis class. Devices constructed in this class can also be used in general chemistry laboratories. We describe the design, construction, and laboratory instructional application of a simple computer-controlled, constant-pressure calorimeter. The calorimeter was made using a covered Styrofoam cup as the reaction chamber. A thermistor was used as a temperature-sensing element and was incorporated in a temperature-to-voltage converter circuit based on a bridge amplifier. The instrument was interfaced
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to a personal computer via an I/O board, and data acquisition software was used to monitor the output voltage of the bridge amplifier. Students will learn to calibrate and evaluate the performance of the instrument they have built in one of its possible applications: the determination of the heat of formation of magnesium oxide via Hess’s law. Experimental results for the heat of formation for magnesium oxide are within 1% of the literature value. This experiment also demonstrates the utility and ease of automating temperature measurements for other applications. Hazards Magnesium reacts readily with dilute acid, liberating hydrogen gas. Avoid the use of acid more concentrated than that recommended in this experiment. Avoid exposing magnesium to flame sources or high-temperature objects because it is flammable. W
Supplemental Material
The full text of the laboratory experiment with figures is available in this issue of JCE Online.
Journal of Chemical Education • Vol. 78 No. 6 June 2001 • JChemEd.chem.wisc.edu
