UNDERGRADUATE ORGANIC LABORATORY CHEMISTRY ZVA. Ted-tube Experimenfs
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E. F. DEGERING Purdue University, Lafqette, Indiana
The purpose of laboratory instwction i s twofold: "to learn" and "to learn to do." Thefirst has to do with the acquisition of experimental knowledge, whereas the lalter i s concerned with the development of correct experimental habits or "laboratory technic." The amount of experimental knowledge acquired from any given laboratory procedure i s dependent upon the ty@ of procedure, the method of instruction, and the student concerned;
but the laboratory habits that the student a~puiresare largely the result of the particular manipulative practices inwolwed. To encourage the student "to learn" the maximum amount in the allotted time calls for carefully selected experiments and adequate instruction, but to teach the student "to learn to do" c d s for appropriate and very carefully prepared procedures and thorough supervision.
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distinct purpose in so far as it can aid him in his desire "to leam to do." This dual objective, it would seem, serves as the unanswerable argument in favor of laboratory instruction. The student learns, for example, through his visual sense from his textbook or through his auditory sense from his lecture routine. The material thus acquired is intangible and irrelevant in so far as the actualities of life are concerned. Let us assume that through
T THE outset, the ultimate purpose of laboratory test-tube experiments should be clearly set forth. Such exercises should serve to span two distinct gaps in the student's training. To illustrate, let us read into the old adage "we learn to do by doing," the dual meaning expressed in the phrases "we learn" and "we leam to do." The laboratory serves a distinct purpose in so far as it can aid the student in his &art "to learn" and it likewise serves an equally
factual knowledge he has learned that sodium reacts with dry alcohol in the cold but that it does not react with dry ether under similar conditions.. Aside from a mental notation, this particular item means little or nothing to him, even though his instructor may have taken considerable time to explain the difference in the behavior of the two substances. Why? Because, barring laboratory acquaintance, the average student knows very little about any of the three substances concerned and proportionately less about what might be expected when any two of them are brought together. Of course, we must always allow for the student with an adequate imaginative set-up to visualize the problem in its entirety; but the average student gropes about, with the abstract fact fluttering hither and you in his mind in quest of an adequate association or correlation. Given an opportunity in the laboratory, however, to add small pieces of sodium to small amounts of dry alcohol and dry ether in each of two test-tubes the student assumes the r81e of an investigator and is immediately confronted with certain facts that demand explanation. He observes that the alcohol reacts with the sodium and evolves a gas; the ether does not react with the sodium. The student now knows by first-hand information that there is a distinct difference in the reactivity of these two substances with sodium; but here again the instructor encounters a very difficult task. Too many students are satisfied merely to know that there is a difference or to note what particular difference is involved. Far too few are concerned with carrying this particular phase of the problem to its ultimate conclusion. Why did the alcohol react? Why did not the ether react? Only with these questions, consistently answered, has the student acquired by practical experience an additional bit of information which will be retained as a part of his actual experience. While the responsibility for the adequate solution of the problem falls upon the instructor coucerned, there are doubtless certain practices that materially aid the student in feeling his way. GrAphic and balanced equations, whenever possible, are invrduable aids in the visualization of fundamental differences in the symbolic structures of compounds and their corresponding properties. Appropriate labeling of precipitates, gases, and immiscible liquids serves as an additional aid in the visualization of characteristic reactions. Finally, interpretations, correlations, and conclusions all compel the student to fortify his position. The problem of teaching the student "to learn" lies within the grasp of the instructor in so far as he may select appropriate experiments and the use of adequate methods of instruction. But in so far as the selection of his students is concerned, the instructor must, for the most part, take what his constituency wills him. For the student of science, the second phase of our problem is equally important. The mere performance of certain tests in the laboratory as an aid both to the memorv and to a clearer comprehension of the twic concerned is far from adequate. Aside from acquiring
the ability "to learn," the student of science must acquire the attitude which compels him "to learn to do;" for it is by virtue of the latter art, no less than the former, that science has made its progress. I t is in the performance of just such simple things as test-tube experiments that the student acquires, bit by bit, an appreciable training in the fundamental habits of laboratory technic. Many of the test-tube experiments in organic chemistry are a little di5cult to perform because of the non-positive character of many of the results. Hence the student must early acquire the habit of being all eyes and ears and nose at all times; for changes in temperature, in color, in odor, in miscibility, in volatility, in solubility, and numerous other properties are all clues that lead him on in his quest of the unknown. Realizing that there was an essential training in laboratory technic to be obtained from the correct performance of test-tube experiments, the author sought means of intensifying this training. One decided step in this direction in our laboratory, after careful preliminary experimentation, was the adoption of two-inch test-tubes for all laboratory test-tube experiments. The results have been gratifying. The mere fact that the student is dealing with only a few drops of the substance under examination seems to awaken in him a realization that he must be alert if he is to obtain any benefit from the experiment. The use of such small amounts demands more careful procedure on the part of the student and much more careful observation of what takes place. Unconsciously, the student acquires better laboratory habits. Though the additional training the student receives in proper laboratory habits by ,+@useof two-inch testtubes more than justifies their use, there are additional arguments. Two-inch test-tubes cost less than the fiveinch test-tubes and can be stored much more conveniently until the respective tests have been approved by the instructor. (It is our practice to have the student save his test-tube tests until the exercise is completed, at which time they are checked and approved.) The use of two-inch test-tubes in place of five-inch test-tube involves an appreciable saving in chemicals. The student normally works with about onefifth to one-tenth the amount he would use in a fiveinch test-tube. Even though instructed to examine 1 cc. of a liquid, the average student will use three to five cc. if the test is to be carried out in a five-inch test-tube. Repeating the same test, however, in a two-inch testtube the same student will be more careful of the amounts of the compounds and reagents used. In a subsequent article on ultimate qualitative organic analysis, a procedure will be presented in which two-inch test-tubes are used as standard equipment. In conclusion, it is apparent that test-tube experiments serve two very important purposes in the student's training; they aid him both "in learning" and "in learning to do." But the art of "learning to do" is appreciably intensified, in the opinion of the author, by the use oftwo-inch test-tubes. -
