DONNABOGNER
Wichita State University Wichita. KS 67208
Take Your Choice: An Intuitive and A DemonstrativeApproach to Stoichiometry The following manuscripts, both focusing on the teaching of stoichiometry to first-year chemistry students from very different perspectives, found their way to this editor's desk a t the same time. I t was decided to publish these articles in the same column for the convenience of teachers who are looking for new methods of presentation and to emphasize that effective introductions to abstract chemistry concepts can take very different approaches.
Teaching Stoichiometry
The problem was presented as follows. Let us assume two chemicals, which we will call A and B combine to form a new chemical, A-B. This can also be written A B A-B. Let us also assume that 1 dozen atoms of A weichs 1 nound and " 1 dozen atoms of B weighs 2 pounds. The instructor may want to mention that these atoms are make-believe and that real atoms are not that heavy. After explaining that one atom of A combines with one atom of B, the author asked his seven-year-old daughter, "How many dozen atoms of B do we need if we have 1dozen atoms of A?" When the correct answer was given, multiples and even a half-dozen atoms of A were attempted. She was then asked how we could be sure we had the correct number of atoms if they were so small we could not see them. She came un with idea of weiehine" out twice as much B a s A so we would have the same number of atoms of each and then she solved afew weieht nroblems. sucbas how manv ~ o u n dof s B are needed for = & e n number of pounds of A. 'Finally, she was able to switch eaiilv from "dozens of A" ro "pounds of B". No ratios or algorithms were used; she ihtuitively "knew" how and when to do the conversions, and her answers were always in the correct units! The final step in the experiment was to change the chemiB-A-B. With questioning, the cal equation to: A 2B seven-year-old deduced that now twice as many atoms of B were needed to react com~letelvwith A. Some of the author's coileaguis will object to telling someone that atoms can be weighed in pounds. Also, he will admit that a one-on-one situation is always pedagogically superior to a lecture situation. However, if a seven-year-old can grasp a concept that is historically the "most difficult part of the bednninaclass" themethod must be effective. Note that the auihor emphasized the word concept. We need not get bogged down in formulas, terms, and "absolute correctness" if our goal is teaching ideas and conveyiuginformation.Once the idea is discovered, a highschool or college student should be ready to make the jump to moles and Avogadro's number.
+
+
Richard P. Steiner
University ol Utah Salt Lake City, UT 84112
Over the years much has been written about the difficulty of teachine the mole concent to students.'.Z In fact. Dierks. Weninger, and Herron recently wrote:
-
Historically, teachers of beginning chemistry have named the mole concept as the most difficult part of the beginning course.3 It is possible that the reason for this difficulty stems from the following: (1) We introduce the topic with the horrendous new word
"stoichiometry". We divert attention awav from the oroblem at hand hv, usine.. chemical equations xith'which stu&nts may nut be familiar. 13, W e intn,dure anuther new term r m d e ) anda numlrer s
