edited by
J. DUDLEY HERRON Pvrdue University West Lafoyene, Indiana 47907
The Mole Concept Perhaps no concept in chemistry is more basic or more difficult for beginning students than that of a mole. In this issue of High School Forum we present ideas which have helped two teachers place mole in the minds of their students. We hope that you will try them in your class and, if you have a better idea, send i t along so that we can share i t with those who are still trying to make mole as easy as dozen.
Teaching Moles is Child's Play The following idea is abstracted from a brochure prepared by Donald F. Clausen, University of WisconsinStout. Students are told that they are working for a toy manufacturer. Under design and development is a doll's dress and a toy garage. Mock-ups are presented in the form of a cardboard cutout of the dress with buttons glued on and a wooden garage nailed together with four 4-penny finishing nails and six 3-penny box nails. The doll dress requires 3 large buttons and 2 small buttons per dress. Students are told that others in the firm are responsible for design of the dress and garage. Our responsibility is to buy the proper numher of buttons and nails. Sales tells us that they can sell 100,000 doll dresses and 100,000 toy garages. Since the prohlem is the same for hoth articles, only the example of the doll dress is used here. However, in the classroom the redundancv of workine both exam~lesis heloful. I t is immediately eXdent that d a ~ af millfon buttons will be reouired for the 100.000 doll dresses:. 300.000 . of the l a r-~ e size and 200,000 of the small size. The question is how to order them, receive them, and know that we are getting what we pay for. Sooner or later a student will suggest that there must he a relationship between button weight and the number of buttons. The instructor then offers the sueeestion that the calculations be done in terms of 1000 buttons and suggests the name of "toymole" to refer to 1000 units. Since the large buttons weigh 0.4 n each, 1000 of them weigh 400 g or 0.88 lbs. The factory obviously needs 300 "toymoles" of large buttons which weigh 264.3 lh and cost, at $11.35 per lb, $3,000. Using similar calculations, the cost of the small huttons is calculated, The calculations are done using English units to strengthen the student's understanding of the relationship between the metric and English systems and t o ensure that the example is meaningful to those students who are not yet able to think in terms of metric units alone. Editor's Note: Contributions in High School Forum from high school teachers are especially solicited. Some teachers may feel that they have more questions to ask than answers to give. These are also invited. Send two copies of all contributions ta the column editor.
After the calculations are completed, the instructor points out that the use of similar units is commonplace. For example, we buy shoes by the pair, eggs by the dozen, and paper by the ream. As things get smaller and smaller, the number of them per unit gets larger and larger; shoes are heavy and come in twos, eggs are lighter and come in twelves, paper is still lighter and comes in 500's. Our small buttons and nails come in 1000's. In order to transfer the idea to atoms and molecules, the instructor points out that atoms are uery small and that the unit used to discuss them is uery large-much larger than the 1000's in which the buttons and nails were measured. I t is pointed out that 1000 atoms or molecules would be much too small to see or to weigh. The real mole is then introduced as the number, - 602,00~000,000,000,000,000,000 (or 6.02 X loz3). Comparisons are then made between the weight of a "toymole" (1000) of large buttons (400 g) and the weight of a "toymole" of small buttons (150 g). The discussion then moves to the weight of a mole of hydrogen atoms, carbon atoms, and ultimately to the weight of one mole of various molecules.
The Mole Calculator The following idea was suggested by Howard F. Heup, Fox Valley Lutheran High School, Appleton, Wisconsin. The "Mole Calculator" (see figure) is a learning aid that has been used successfully a t Fox Valley for four years. I t has been used with high school students of average to above average ability at all grade levels. In the early stages of learning the interrelationships between moles, molecular weight, and the molar volume of a
The mole calculator.
Volume 52, Number 11, November 1975 / 725
