Should the Mole Concept be X-Rated? Henry A. Bent North Carolina State University, Raleigh, NC 27650
Yes! It's annihilating interest in chemistry. And what a pity that is. All that dry drill on crabbed mathematical detail is destroying many people's enjoyment of a splendid subject unnecessarily. For, Those who are not going on in chemistry don't need the mole concept. And for those who are going on in chemistry, the mole concept is as easy as rolling off a log, once one knows what log it is one is rolling off of, from a year or so of tramping about with an experienced guide through the fascinating forest of chemical transformations pictured atomistically. For, The mole concept is merely common sense applied to a n atomic model. (see Insert). But, you say, ask college teachers, What is it you want us to teach our students?, and thrv tell us.Teach themone rhina: the mole concept. Well, All right then, spend a day or so, in class, on the mole concept. Some students will see it right off. Certainly prospective chemists should see it easily, else they should he prospecting elsewhere. Most of the others won't need it. And those that do will see it again, when they've greater readiness for it.
computers, to paraphrase the 19th century Russian pedagogue Ushinsky, should be done mechanically, with computers. Save class time for chemistry that cannot he done mechanically with computers: real-time, real-life chemical transformations. I n the end, it's not the absolute level of knowledge that students have acquired that is important. Much detailed knowledge is soon forgotten. In the long run, what's important is their enthusiasm. Anything that endangers student's enthusiasm should he x-rated.
Commonsense Arithmetic of Amount Units of amount, n,are, e.g.: pair, dozen (dm),mole (mol), and elementary entity (ee). The number, N, of elementary entities per each unit of amount is: 2/pair, 12/dazen, 6.02 X 1023/mol,l/ee. Those ratios are equal to each other: 2 12 6.02 X loz3 = -1 = -N -=-= pair doz mol ee n (1) (2) (3) (4) ( 5 ) = Nn (Avogadro's Constant) Checks (by the Greek rule of cross multiplication): From (1)and (2): 12 pair = 2 doz From (3) and (4): 1mol = 6.02 X loz3ee Also, from (3) and (5):
But above all, Do no harm. Don't destroy interest in chemistry. Don't try too hard. Relax. Enjoy it.
N (number of elem. entities) = 6.02 X = 6.02 X
loz3X (nlmol) loz3 X ("amount expressed in males")
But that's not rigorous! Ah, said Matthew Arnold, then rigorous teachers seized my childhood. Poor childhood. Poor is the child's readiness for reading whose preparation for reading has been chiefly (rote) reading. Poor is the student's preparation for college chemistry whose pre-college chemistry has been chiefly college chemistry. Poor is the student's preparation for using the mole concept in chemistry whose concept of chemistry is chiefly the mole concept. The mole concept in chemistry is for mature students of chemistry. Like the dozens concept in daily life, it's a waste of time to try to teach the mole concept to a person before they have learned to think atomistically about the corresponding sense impressioos-and almost trivial to teach thereafter. For the mature student of chemistry, the mole concept can he taught, can perhaps best he taught, mechanically, with computers. And that which can he done mechanically, with
To allow for m (moton) Z rn (neutron). m (electron) f 0. isotopes,and packi'ng-fraction effects, use tabulated "a&& weights."
Approximate Masses and Molar Masses m (proton) u rn (neutron) >> rn (electron) m (6.02 X loz3nucleons)
-- 1g
That, in a nutshell, is the story of amount and mass in chemistry. The rest is episodes.
Example: Molar Mass and Elementary Composition of Water Counting nucleons, one finds that rn (6.02 X loz3HzO malecules) 18 g.IThe fraction of water's mass due to hydrogen is:
-
2 X 100 2 2 100 -18 -=x-=-= 18 18 100 100
11.11 Per
cent,
= 11.11"percent"
