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a& t4e N e w England Association of Chem
Jay A. Young
King's College Wilkes-Barre, Pennsylvania
chers
Practice in Thinking
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previous publication1 described a new approach to the elementary laboratory. Laboratory problems, from simple to complex, are assigned to each student or pair of students. They solve an assigned problem by developing and testing a hypothesis related to the phenomena observed when the steps described in their problem are carried out in the laboratory. The major emphasis is placed upon the conception of a plausible, testable hypothesis, and upon the procedural steps taken to carry out the test. In general, students respond well to this approach since it gives them an opportunity to meet a challenge that is within their ability to surmount. The answers to the assigned problems are not furnished directly by a laboratory manual or on a previously specified page of a text or reference book. Hence the students must read rather widely and diligently to find the desired information. As a result information is learned; some real thinking is done, both in the conception of a testable hypothesis and in the effort to devise a test of the hypothesis. Examples of the problems assigned to students have been given in the previous publication' and a complete list of problems is available2 but one example can be cited here. A small piece of aluminum foil is clemed with benzene to remove any residual grease that may be present on its surface and is then burnished lightly with steel wool. The foil is partially immersed in a solution of mercury(I1) chloride and, upon removal from this solution, a white growth forms on the foil. The student is asked to explain why a white growth forms on the foil (he is not told that the white substance is aluminum oxide; this is left for him to find out by further study). The observed phenomenon is sufficiently interesting in itself to excite the curiosity of all but the dullest students. The typical student will readily turn to his text and other available references in an effort to find an explanation. Usually, the explanation offered Adapted from the Shawinigm lecture presented during the twenty-first annual summer conference of t.he NEACT, August 17-21, 1959, at the University of Connecticut, Storrs. J. A,, J. CAEM.EDUC.,34, 238-9 (1957). YOUNG, 'YOUNG,J. A,, "Practice in Thinking," Prentice-Hall, Inc., Englewood Cliffs,N. J., 1958.
hinges upon the statement that some of the mercury(I1) chloride is reduced by the aluminum, and the mercury, so formed, amalgamates with the aluminum in the foil. The amalgamated aluminum then reacts with the oxygen in the air to form white aluminum oxide. There are several possible tests for this hypothesis, of course. A student can show by qualitative tests that aluminum will indeed reduce mercury(I1) ions while it is itself oxidized. Or, the existence of an electromotive force, in the proper direction, generated by the AI-Hg++ couple can be confirmed. Or, as one student suggested, the change in weight of the aluminum foil, after a few minutes immersion in the mercury(I1) chloride solution, can be measured, and after suitable heating to drive off the mercury residing in the foil, the weight redetermined. From data such as these the student who attempted this approach hoped to show that the weight of mercury that amalgamated with the foil was chemically equivalent to the loss in weight of metallic aluminum. The procedure was not effective because aluminum oxide formed on the foil while it was being weighed. In a second attempt, the amalgamated foil was placed in a conical flask and the flakes of white substance were collected and saved as the reaction proceeded. Ultimately, the residual, unreacted aluminum was weighed and the weight of aluminum present in the white substance determined by a colorimetric measurement. The weight of aluminum found in the flakes agreed within 5% with the loss in weight of the foil. In a third attempt, a stoppered conical flask was used, and the weight of aluminum in the white subst.ance, assuming it to he aluminum oxide, agreed within 3% of the calculated quantity of oxygen present in the air in the stoppered flask. Although the original hypothesis was not thoroughly tested by this procedure, the results of the tests that were performed did not contradict the hypothesis. The student concluded that his hypothesis was valid within the limitations of his investigation and turned his attention to another assigned problem. This student learned more about the chemistry of aluminum, colorimetry, the behavior of gases, and other topics than has been indicated explicitly here since be necessarily studied many texts and references in order Volume 37, Number 2, February 1960
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to acquire the information that was used to form his hypothesis and to test it in the laboratory. Although he did discuss his problem with several of his classmates and upperclassmen, he did not seek specific help from these others. This action is typical; students sense a personal challenge and seek only generalized assistance from others. In this case, since the student was unaware of the technique, the only specific recommendation received was from the instructor, who hinted that aluminum might be determined colorimetrically. This suggestion was not requested by the student until he had, himself, found that the amount of aluminum oxide formed in his procedure was too small to determine gravimetrically with sufficient precision. The student had previously worked on other, less complicated problems. It has been found that poor students are discouraged by a problem of this complexity when it is assigned to them as the first or second problem to be solved. Since students of limited ability cannot easily be identified early in the year, the complete list of problems for which a student is responsible is assigned to him in the beginning of the semester; a t least two of these problems are not complicated. The more proficient students usually solve these quickly and proceed to more advanced challenges. Students of average ability find their experience with the simpler problems helpful since usually all they need is personal experience with a method of approach that is so very new to them. Once they understand the general approach to be used in solving a problem they are able to continue a t a satisfactory pace, occasionally surpassing their originally more proficient classmates. The very poor students show up sharply as poor students. When a cook-book, fiU-in-the-blank manual is used the poorer students can often bluff their way
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through the laboratory. This is not possible with this procedure and, were it not for the fact that some of the more glaring deficiencies of the poorer student are brought to light by this method, t,he results with poor students would he very discouraging indeed. At it is, however, because their weaknesses are clearly exposed to the instructor, some of the poorest students can be helped, if not to continue in chemistry, a t least to continue in some other major study for which they are better fitted but in which they might well have failed had their habits of study and reflection not been corrected. It is a platitude that a teacher cannot force learning upon a student. Somehow, the student must be persuaded to teach himself. Basically, the method described here depends upon the principle that man, by nature, is curious and that a challenge that excites curiosity can he given, even to a beginning student. And if the student himself can foresee that the challenge is not beyond his ability to solve, he will meet it successfully and willlearn in the process. The teacher's task is thereby reduced to its proper dimensions, to guide the order of acquisition of knowledge in accordance with the progress of the student as he learns. I t is also a platitude to &ate that it is uurealistic and improper to allow the student to infer, from the met.hods we use in teaching, that chemistry is best learned by rote and by cook-book methods. The student must learn that chemistry is a vital, real subject, in which many answers are stiil unknown. Perhaps the beginning laboratory course has been the greatest offender in this respect, but it is also true in some other courses that we teach. What has been outlined here is only a beginning. A similar approach can he used in other courses.
