A Logic Diagram for Teaching Stoichiometry In the ~ a r l "pnrt of an intr~durturyCOUISC in chemistry, afler nlomir theory and atomlc weqhts are introduwd. the studenr is usunlly emfnmrcd with a host of sruichiometric valct~latimsinvolving ~ u r h terms as: formula, formula weight. percent composition, pmp~rrcalformula and empirical fwmula weight. I have found the following diagram helpful in teaching the fundamentals of staichiometry. We define the following terms
GRAM FORMULA WEIGHT
GAW = Gram atomic weight GFW = Gram formula weight
m- m m e a n s : "If A is known, then B can be determined." L m m e a n s : "If /. and x are known, then B can be determined." ( X = GAW or GFW) means: "If A, B, and x are known, then C can be determined."
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GRAM EMPIRICAL FORMULA WEIGHT
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For example, the diagram suggests how a knowledge of the gram formula weight and the empirical formula together with a table of GAW's is sufficient t o determine the formula of a compound. Similarly, given the formula of a compound and the GAW's of its elements, the gram formula weight can be calculated, etc. It should be noted that "one way" and "two way" logic paths occur in the diagram. Thus one can determine the gram empirical formula weight from the empirical formula using a table of GAW's, hut not conversely (a "one way" logic path). However, a "two way" logic path exists between the percent composition of a compound and its empirical formula "ia the GAW's. The diagram may he used both to introduce and t o summarize stoiehiometric concepts, but i t is particularly useful for classroom problem sessions in which the teacher solves problems and shows how t h e logic in working problems is revealed in the diagram.
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University of the Paeifie Stockton, California 95204
492 / Journal of Chemical Education
John R. Tyndsll
