What Should Students Do
in the laboratory?
I
provocative opinion
As
distinguished from many students in the laboratory, the chemist at the laboratory bench is stimulated by a challenge. I submit that it is our intuitive recognition that students ought to be doing much more than manipulating apparatus, and our perhaps not well recognized admission that we have not in the past really tried to measureably discern if they are doing much more, which has caused the present furor over the validity of the laboratory as a suitable educational device. Whether or not a student will become a chemist or other scientist, some of his work at the laboratory bench ought to he initiated by challenges, and his responses to those challenges more precisely evaluated. Without doubt, the common practice of presenting the student with an exoerimental ulan designed bv someone else (such as the author of a laboratory manual) is a valid means for teaching principles and techniques, and for showing by example how a laboratory procedure is designed to fit an investigation, while helping the student to gain confidence in his own handling of apparatus. But its further applicability seems to be limited; the student from the freshman year onward also needs opportunities to design his own procedures, if the challenge which can be given to him, which initiates his own investigation, is to be properly satisfied. This answer to the question posed in the title is intended to stimulate further discussion. It should
Laboratory work a t the graduate level is exchded from this disenssion; in that milieu atndents also ought t,o address bhemselves to the more sophisticated problem: How to pose a significant and answerable qnestion. Of course, some of this might well be begun it, rmdergraduate laborat,ory work. Objectives whieh cannot be behaviorally identified with canfideuee include: (1) acquisition of the habit of safe laboratory practice, (2) recognizing consistently when it is desirable to memure t.o only a few significant fig~lres,and when instead care must be taken, and (3) s p o n l a ~ ~ e a rexclamations, ~s voiced or silent, whieh indicate esthetic sensitivity for an exciting or beintt i f d phe~romenon,or ior the well-planned work of another st,udent,. The process iends to be cyclic, the further work, item 6, produce3 more descriptive facts (obtained by observation), requires manipulation of apparatus, yields data which when interpreted, m d reported, wggest more lab work, and so on. (:enerally, n freshman can tolerate two cycles; the first,, a brief rook-book "demolrstratiau," and the second involving his own experimental design. This paper is restricted largely to a desrriptim of freshman laboratory instnrction. For upper division laborat,ory objectives see YOUNG,JAYA., J. CHEM. Eouc., 43, 120 (1066).
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therefore include both the several currently accepted objectives of laboratory instruction and indicate practical means to achieve these, in some kind of measureable way. This answer is proposed: in the laboratory the student ought to teach himself how to answer questions which can be posed to nature at t'he laboratory bench.' Currently accepted objectives of laborat,ory instruction include a few which cannot be behaviorally described with confidence, and others which can be so described, hut, even so, are not always made explicit to the student nor used to evaluate his work. i\Iy thesis can be stated: Unless, where possible, specific behavioral objectives implicit in a statement of laboratory purposes are recognized by the student as t,he criteria upon which his performance is evaluated, these purposes are not likely to be f~lfilled.~Indeed, in such cases both students and professors may well view the laboratory as non-productive. Each of these behavioral objectives can be understood by the student and their degree of arhievement, at least qualitatively evaluated by the professor: (1) to directly acquire some descriptive chemical knowledge and organization of this knowledge with other descriptive information obtained from books, (2) to manipulate reagents and apparatus so that a reliable measurement or observation can be made, (3) to observe critically, (4) to interpret data, (5) to present a clear exposition of the interpretation of the data, and (fi) to plan and carry out further laboratory work which will extend and amplify these data and their interpretation." I suggest that emphasis upon the sixth objective strengthens the achievement of all of the others, and, further, that by this emphasis the student becomes aware of and accepts a challenge to initiate and carry out a piece of laboratory work of his own design. Or, to restate the practical objective which encompasses each of the other objectives: To design one's own experimental investigation in order to answer a question about the chemical behavior of substances. Laboratory work is of lesser consequence to the student unless the data he obtains are at least in part new t,o him, or are obtained by a procedure which includes his own experimental design or his modification of a design suggested by others, or all three. Succinctly, significant laboratory instruction is achieved not only if the student knows how to titrate, but also while he decides whether to titrate (in a particular instance) instead of using a calorimeter or other technique-and if his decision is to titrate, also while he chooses to use a 50-ml or a 5-ml buret, or a weight buret, or to merely count d r o ~ s .
Laboratory bench work involves the preparation to measure or observe or the measurement or observation of volume, mass, temperature, color, heat (occasionally), photon flux, differences in photon flux, the flux of other particles (beta radiation, etc.), electron flux in a conductor, potential difference, time, length, angular magnitude, area, and arbitrary units (bubbles or drops). Each of these measurements or ohservations and the preparation for such can be made using many kinds of instruments, each differing at least a little in their principles of operation and in the techniques used. Mastery of these devires, alone, defines the technician. I t is the proper combination of these, along with suitable reagents and appropriate consecutive time-order and space-arrangements which identifies the chemist at the lab bench. Practice in the art of proper selection of sequences of operations, so that appropriate observations and measurements can he made and interpreted should be emphasized in laboratory instruction. An example will illustrate the significance of this selective aspect. In his work on the behavior of iodine dissolved in carbon tetrachloride, Hildebrand obtained indirect evidence that at high temperatures the iodine-carbon tetrachloride system probably existed in two phases. It was quickly established that the system was too opaque to permit visual or other optical examination which would directly disclose the state of the system. Ultimately, the question was addressed by placing iodine and carbon tetrachloride in a sealed glass tube held in an inclined position on a pivoted rradle and counterbalanced by a small spring. As the temperature of the system was increased, the sealed tube tilted further as indicated by a beam of light reflected from a mirror attached to the tube at its pivot point. This fact empirically established that at high temperatures the system existed as two phases, one more dense and iodine rich, the other less dense and iodine poor.4 Note that in designing this experiment, from the whole set known to him, Hildebrand selected a sub-set of techniques, knowledge of chemical facts and chemical principles. The design of any experiment requires that the designer select only some of that which he knows or can do, and that this limited, sub-set then be applied to the question under investigation? Probably, proficiency in selecting a suitably a p propriate suh-set of reagents and apparatus cannot be taught. Indeed we can teach descriptive chemical knowledge and laboratory techniques; students today are generally aware that their abilities in these matters are evaluated. We can encourage critical observation, data interpretation, and report writing; and evaluate
' Hno~nR!mo,JOELH., Science, 150, 444 (1965). It is interesting to note that this same criterion, the selection of a suitable snb-set of techniques and knowledge from the whole set which is available to the individual, applies to any human work, except far the very simplest of tasks. In particular, when a uniquely appropriate suh-set is selected, and when the work produced has far-reaching implicstions, it is identified as a masterpiece, partienlady in t,he fine arts. In this respect at least,, science is remarkably similar to the fine arts! We speak of an elegant experimental approach, or of rigorous derivation, rather than using the word, masterpiece, bnt the essentials are the same. ' YOUNG,JAY A,, "Practice in Thinking," Prentice-Hall, Inc., Englewood Cliffs, N. J., 1958; also see J. CHEM. EDUC., 34, 238 (1957) and 37, 105 (1960).
some of these, as most students are aware. So, probably, we can assert that we teach these also in the undergraduate laboratory. But if the student is to become competent in the laboratory, somehow he must learn how to select the most appropriate from all that he knows or can do and we must evaluate his ability to select a sub-set. If this is true, then part of the laboratory instruction, in addition to the other objectives, must include some challenges which require that each student himself select a sub-set from all that he knows. This kind of activity is more readily self-stimulated than exteriorly stimulated, by another individual. Hence, the lahoratory questions to he asked of nature must he personalized, must "belong to" the student-as though they were his own. Of course this sixth objective can be emphasized, and evaluated, only after some techniques and their related principles are mastered, after the student has acquired some descriptive chemical information, after lie has been exposed to a few examples of experimental design which. he can understand and has gained some confidence in his manipulative skill, and after he has had some practice in observation and in evaluating and interpreting data. In the laboratory manual we use; students are directed to carry out a short cook-hook demonstration at their laboratory bench. In the demonstrat,ion some of the facts which can be observed are called to the attention of the student; other facts are available if the student is astute enough to observe them. The student is asked to interpret some of the observed facts by preparing a t,estable explanat,ion which we call an hypothesis. Usually, the hypothesis is obtained as a result of a little or extensive amount of reading of references and the lecture textbook. The question is posed to the student in a specific way, but generalized, it is: Do other facts which can be obtained from an experiment or investigation of your own (or copied) design support your hypothesis or render it questionable? Written reports are always required; occasional oral reports are required, and many informal oral reports are rendered. One st,udent had the problem of determining why a candle wick could be reignited, after the flame was extinguished, by placing a lighted match in the column of smoke which rises from t,he just-ext,inguished wick. He postulated that vapors from the parafin of which he presumed the candle to he composed were issuing from the still warm wick and were combustible when brought into contact with a lighted match. To test his hypothesis he proposed to obtain a sample of the vapors issuing from the wick while the flame was burning. For this, he intended to use a glass tube connected to an aspirator and insert it into the flame near the wick. Ultimately he did use this technique but found it necessary to use a "U" shaped glass tube, collecting the vapors as a condensate by cooling the lower portion of the "U" tube. The student anticipated that he would find the composition of the samples from the two sources to have the same percentage of carbon and hydrogen-which he intended to determine by a combustion analysis. I n a. discussion of his plans, he became aware that the quantity of sample of condensed vapor which he could Volume 45, Number 12, December 1968
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anticipate obtaining from the flame would be quite small and that therefore t.he mass of carbon dioxide and of water from a combustion of this sample would also he quite small. He was able t,o realize as a consequence that the increase in mass of the carbon dioxide-absorbing material and of the water-absorbing material in his combustion train would be very small in comparison with the mass of absorbent. He soon realized that the precision necessary for this determination was probably beyond his ability as a beginning chemistry student. With a further discussion he was ahle to suggest that another test for the presumed similarity between the samples from the two sources would he a measure of their molecular weights. He proposed to determine this by a freezing point depression approach. Up to this point in his search t,hrough t,he literature on the matter, the student's method had been somewhat random. Specific references were suggested to him a t this time; he eventually determined a boiling point range for each sample and of course found that the samples were quite different. Meanwhile, he had learned enough in his other reading to suspect that thermal cracking had occurred and incorporated this additional information into his final written report. In another instance a student observed that a gas is evolved when a piece of magnesium ribbon is immersed in a solution of water saturated with hydrogen chloride but only a very little gas is produced (and that only for a short interval) when the metal ribbon is immersed in a solution of hydrogen chloride in toluene. The student's original hypothesis was a straight-forward assertion that hydrogen chloride ionized in water and not toluene, with the consequent expected chemical activity. With the help ifa few discussions and references to specific sources dealing with nonaqueous chemistry, the student ultimately proposed a more interesting hypothesis stating that toluene is a weaker base than water. By this time he had learned of the leveling effect of water upon strong acids and decided to turn his investigation toward a study of this, rather than to continue with the original phenomenon. Consequently, the student attempted to find an acid which would ionize in toluene a t least to some extent. He used conductivity as the indicating datum and was unable to find any acids which ionized in toluene. Ultimately, he decided to find a solvent which would not level out the difference in acidity between hydrogen chloride and hydrogen iodide. His first selection for such a solvent was anhydrous sulfuric acid but eventually he selected and used anhydrous acetic acid. He ran into some interesting difficulties in his attempt to produce dry hydrogen iodide and in measuring and in manipulating both gaseous hydrogen iodide and hydrogen chloride. In his final work on the topic, he was ahle to show that the conductivity of a solution of hydrogen iodide in acetic acid was substantially greater
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Journal of Chemicol Education
than the conductivit.y of hydrogen chloride dissolved in acetic acid, a t thesame concentration. The final example illustrates a desirable increase in sophistication on the part of t,he student involved. This student was asked t,n account for his observation that when a few drops of water are added to t,he combustion products from the burning of magnesium in air, a sharp odor is not,ed. His initial postulate suggested that gaseous, odorous magnesium hydride was produced by the action of water on megnesium oxide. Data obtained from his experimental design demonstrated otherwise. Next, he postulated the formation of magnesium carbonate in the combust,ion and the production of odorous carbon dioxide when water was added. Eventually, with the help of some rather strong hints and some additional reading, he concluded that one of the products of his comhustion was magnesium nitride to which he ascribed the formula IlgaiYZ. By this time he had learned that magnesium nitride produces ammonia when it is treated with water. His test of his hypothesis involved the weighing of the original comhustion products, the additiou of water, reheating, and repetition of these steps until a constant weight was obtained. From these data, assuming that t,he original product was only magnesium nitride (with the formula he ascribed t,o it) and magnesium oxide, and t,hat the final product was pure magnesium oxide he nbtained t,he atomic weight of nitrogen, calculat,ing it to be 16.98. He considered this atomic weight to be sufficiently close to the accepted value to confirm his hypothesis that magnesium nit,ride was formed in his combustion and has t,he formula ;\lgaN,. (This determination of the atomic weight of nitrogen is remarkably similar to the met,hod by which it was determined, classically; it is almost certain that t,he st,&dent had no knowledge of that determination--as far as it is known he developed it on his own.) I t is possible t,hen, to ohtain more objective evidence t,l~att,he st,udent has or has not achieved the purposes of the laboratory inst,ruction, provided t,hat we are willing to spend our time and effort beside the student at, his laboratory bench and in consultation with him before and after the laboratory session. Since our time is limited (especially for individual students in large beginning courses) we are probably not ever going to be able to really tell for sure if much more than manipulation t,akes place at t,he laboratory bench, but to the extent that it. is possible we ought to t,ry. It seems to me that it is practical t,o look for this evidence as we observe the student a t his lab bench, as we discuss his ideas with him, and as we examine his real laboratory report. Joy A. Young
King's College Wilkes-Barre, Pa. 18702
