A Schematic Summary of General Chemistry Stoichiometry "One picture is worth more than ten thousand words." Recently, a logic diagram for teaching stoichiometry' and a flowchart for solving chemical problems2 have applied this ancient Chinese proverb to some chemical calculations involved in the first semester general chemistry course. The diagram' shows exactly what quantities are required to calculate other quantities, while the flowchart2 includes the actual calculation^ involved in the operations. The appended schematic summary, which I regularly distribute to my first semesbr general chemistry students, combines the advantages of both the diagram and the flow chart and extends their approaches t o a wider variety of problems. Many beginning students, even the better ones, have only a hazy knowledge of the interrelationships between the quantities involved in stoichiometry. While they may he able to solve specific individual problems, their knowledge is fragmented. and the" mav have little idea aa t o how one tvoe is related t o another. A schematic summary permits .. of oroblem . even pkrer studen~qto grasp these important relatiunships at a glance. My general reluctance to emphasizes ..cut-&d-dried" formula approach is more than overcome by my belieithat such achart permits thestudent t o w e "the hig pieture"of stoichiumetry in a more realistic perspective. Roth the 'forsst"and the "treesWareincluded in the chart.
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The schematic summary also emphasizes an approach that I have found useful through the years in teaching stoiehiometry, uiz., problem solving as a "translationn process. Chemical equations, which feature prominently in many types of problems, arestated in terms of numbers of chemical units (atoms,gram-atoms,molecules,moles, etc.), which are given directly by the coefficients. Measured quantities, on the other hand, are usually given in t e r n s of weights or volumes of physical units (grams, liters, etc.). In order to solve problems involving chemical equations, the student often must first "translate" the physieol quantities of everyday reality or laboratory measurements into the chemical units that can be manipulated directly in the equation and then "translate" the answer from chemical units back into the physical quantities of everyday life. A similar useful and up-to-date analogy is that of computer language. The everyday physical quantities must first be " .~ r m .. a m m e d "into comouter lanewee - .(chemical units) so that the eauatbn can deal with these data. The eouation uroduces i u answer in computer language tchmxienl units), which must then be "translated" back into everyday ph)aicol language. In the achematicu~~mmnry, plz\wal quantities are enclosed hy solid lines and rlwmirol quantities by dotted lines. Tyndall, J. R., J. CHEM. EDUC., 52,492(1975). Ryder, R. G., Chemistry, 48(8), 240975). California S t a t e University Fresno. 93740
George B. Kauffman
Volume 53,Number 8,August 1978 / 509
