This experiment determines the stoichiometry of the reaction of a carbonate or hydrogen carbonate and HCl by measuring the pressure of the CO2 produced using a Vernier pressure sensor, Texas Instruments CBL interface, and a TI-82/83 graphing calculator. Various amounts of the carbonate are reacted with a constant amount of HCl. The change in pressure in a constant-volume (20-oz soda bottle) system is measured and plotted against the mass of the carbonate. The mass of the carbonate that is needed to react with all the HCl is determined from the graph. The mole ratio between the carbonate and HCl in the reaction mixture is determined and used to write a balanced equation for the reaction. Different carbonates and hydrogen carbonates have been used successfully. The advantages of this procedure are that students can run a large number of samples (since each sample requires only 100 s of data collection time), develop an understanding of the concept of a limiting reactant, and develop an understanding of the relationship between the amount of gas produced by a reaction and the pressure in the reaction container. The experiment incorporates the use of technology, graphing, and data analysis and is appropriate for an introductory chemistry laboratory. The directions can be easily modified to use computers and other graphing calculator probe systems.
Supplement
A student handout, instructor notes, instructions for the TI-82/83 program, INTRSECT, and the program itself are available as supplementary material. The student handout, instructor notes, and instructions for the program can be accessed as a pdf file using Acrobat Reader or as Microsoft Word documents. The INTRSECT program has been provided by the author for both Personal Computers and Macintosh Computers. The text files and the programs have been compressed into sit (for Macintosh) and zip (for Windows) files.
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