James D. Wheeler, S. J. Rockhurst College, Kansas City, MO 641 10
How do we get students to pay atcention todetails without losine sizht of the furest for the trees? asked a question on a General Chemistry test AH I of formation (standard conditions) for carhon monoxide gas is -110.5 kJ per mole. The comhustion of carhon monoxide (CO) to produce carhon dioxide yields 283.0 kJ/mole. What is the standard heat of formation per mole for carhon dioxide? With one "small" excention. this nrohlem should have been a "gift." The students had learnedthat for exothermic reactions delta H is neeative. so when the combustion process is said to yield 283.0k~,thk only thing noticed was the ahsence of the negative sign, and a large proportion of the students wrote: C + 112 O2 = CO -110.5 kJ CO + 112 O1 = COa 283.0 kJ C + 0% = COZ 172.5 kJ When auestioned afterwards, several students admitted that they know that comhustion means hurning, and burning is certainly an exothermic reaction. Have they been so trained that there are consecrated modes of expression which one must look for and ignore the context? They were unable to sueeest whv thev missed these. other than to sav that the value was not given as negative. Have they been so trained that there are only these certain phrases and no others? Yes, I think so--If the prohlem has "X" in it, then i t fits "formula 2." However. I think there is more than that. I do not really think it is matter of attention to one or a few details, hut rather, they have been taught to look for certain "sign posts," and, for all practical purposes, to ignore all else. The heat of reaction is given as 283.0 kJ, therefore it is positive, and proceed from . - ~ there! ~ ~ ~ ~ ~ Is the following another manifestation of the same problem? The directions for writine the lab reoort as -eiven at the heginning of the laboratory manual read (for part 2 of the report):
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A
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a
w
(2) A precis of the laboratory procedure. This should ordinarily be 100 words or less. . ..
Several students headed part 2 of their report "Precis." Suspicious that they did not know the meaning of the word, I wrote in the margin, "Do you know what this word means?" After I had returned the reports one student came to me, lab hook and paper in hand, and with some indignation said, "You wanted to know where I got that word. Right here in the lab hook." He had to read my notation twice, and aloud, before he recoenized what I had written. ~ n o & e rexample. An early experiment calls for adding barium chloride solution to potassium chromate solution; ronrentrations of hoth are known; the balanced equation has heen written: and the amount of each required by the stoichiometry has heen calculated. The inst&tions then rontinue: Measure out ahout 80wc of the calrulated amount uf barium chloride solutim and add it to the chromate. Then add more barium chloride, 5 ml a t a time, until you are sure the precipitation is complete. How can you tell? 1004
Journal of Chemical Education
T o this question, I get such answers as "When no more precipitate forms." Only very rarely do I get the response, "When the solution is no loneer They have already - vellow." . had quite a hit of instruction in lecture on stoichiometry and limitine.. reaeent. In fact. when I trv to draw out this obvious .. answer, hy asking several more questions, trying to fnrus on solution color, many students hewme impatient and, in ~ffect, just give me the anBwer and let me learn say, "Why don't it, instead of all this messing around?" That the student might be able to figure out the answer himself does not seem to occur to him. Or if i t does, such possibility is immediately rejected, because that's not what learning is. Learning is "Give me the answer, and I'll learn it!" Another case in point. The text I am using has some very perceptive prohlems at the end of each chapter. During one prohlem session with about a dozen students, we had done several prohlems of a particular kind. I noticed one girl seemed to he getting more and more frustrated. She finally said: "If they keep changing how they write the prohlems, how am I supposed to know how to solve them?" My answer was to the effect that we might have to use a certain amount of a trial and error aooroach. and that she should not e x ~ e cthat t the exact .. method for working a particular prohlem should pop into her head immediatelv. And with that. she threw UD her hands and two days later withdrew from the course. Afterwards, she explained to me that she had been taught that all problems fit into certain categories, and as long as 1 was going to keep refusing to tell her what catrgury each prohlem f i ~ into, s she was withdrawing frum my class. 1 present these, not as isolated mses, hut as typical cases. Nor am I trying to hlameany~)ne,andleast of all, thentudent. In fact, it is my firmconviction that thestudent is the innocent victim of i h s\stcm. ~ Nor do 1 blame the student for feeling frustrated. BU--hat can we do about it? "The challenge that school is supposed to give me has only to do with the 'amount of material' that I'm supposed to learn in this course. And expecting me to think my way through a prohlem is unreasonable." "Give me the solution to the prohlem, and I'll learn it," as though all prohlems have been solved. What islare the answer(s)? Is this one prohlem, or several? I am not sure I know. One thing I am going to try is to give this naner to mv General Chemistrv students and wait for comments. And maybe this will prompt a t least some of them to ask for help. And depending on the kind of help they ask for, I can begin to seek some solution(s). Or maybe, it is just that the students need to he made aware of the specifics of the problem-this analysis is a lot different than iust a series of poor grades-and then maybe they will try tdcorrect it in th& own lives, which is what has to happen in the long run, anyway. Note: I did duplicate this essay and pass it out to my General Chemistry students. The only response I g o e w i t h a good deal of prodding-was to the effect that "it is probably true."! Where do we go from here?
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