1444
JOURNAL ox CHEMICAL EDUCATION
N O V E ~ B1928 R,
A GRAPHIC METHOD FOR SOLVING SIMPLE STOICHIOMETFUC PROBLEMS CHARLESH. STONE, ENGLISH HIGHSCHOOL, BOSTON,MASSACWSERS
While the usual method for solving problems in stoichiometry is the best and only method which should he taught to high-school students, it often involves tedious computations. Teachers of elementary chemistry may like to learn of an interesting variant for the solution of such problems. On a sheet of cross-section paper, ruled in tenths, choose a point of origin in the lower left-hand comer and through this point draw two lines a t right-angles. Find next the values concerned in the problem as, for example, 87 grams of manganese dioxide will liberate 71 grams of chlorine from hydrochloric acid. Locate the point 87-71 as is customary in analytical geometry. From this point draw a line to the origin. Now any point on this line will mark the intersection of two perpendiculars, one drawn from a position on the ordinate representing a given value, and the other
drawn to a point on the abscissa representing the corresponding value of the answer. For example, using the accompanying chart, let us solve the problem: "How many grams of hydrogen sulfide can be produced by the action of acid on 50 grams of ferrous sulfide?" The values concerned are 34 and 88. Locate the point as shown. If the answer is to be found in liters, the procedure is the same. "How many liters of ammonia gas can be produced by the action of slaked lime on 40 grams of ammonium sulfate?" The values concerned are 132 and 44.8. Locate this point and draw the line to the origin. For 40 grams of the sulfate the corresponding value in liters of ammonia is 13.5 liters. It is perhaps unnecessary to remark that the accuracy of the results obtained by the use of the above method will depend to a very large extent upon the accuracy with which the chart is drawn.
