QUANTITATIVE ANALYSIS I N THE TRAINING OF CHEMISTS' The "Unit Operations" Approach A. A. BENEDETTI-PICHLER Queens College, Flushing, New York
T H E introductory course in quantitative chemical analysis, with which the following discussion is primarily concerned, has an important function in t,he general training of chemists. I t is widely recognized t,hat, it teaches manipulative technique. For several reasons it is necessary that it provide an efficient introduction to the method of quantitative analysis. Analytical tasks represent a large fraction of all chemical work done, and any academically trained chemist should be able to take part in the discussion of analytical problems and to perform analytical tasks. All chemists should have a grounding in analysis so that they can intelligently evaluate analytical data furnished them for the guidance of their decisions in research, development, production, or sales. The teacher of quantitative analysis faces the dilemma of limited laboratory time and gaps in the knowledge and preliminary training of the students. Seldom have students been introduced to the reasoning of statistics or the meaning and use of significant figures. Their acquaintance with the appearance and behavior of substances and materials is very limited.2 They have little or no experience in glass blowing, the use of basic tools, or the assembling of simple apparatus. Considering the limited time available in one semester of laboratory work, the introductory course in quantitative chemical analysis has a formidable task to perform. Moreover, it must not fail in performing it if there is no assurance that chemistry students will receive additional training along t,heselines.
TEACHING PROCEDURES
What might be called the old type of laboratory training was based upon the performance of a large number of determinations and separations, which could not fail to impart dexterity by repetition. This type of training- requires far more time than that available for the purpose. During the first half of the twentieth century, a feat,ure was added that could be ex~ectedto imorove the efficiency of the laboratory insthction. A &cussion of the equilibria involved and of the precautions dictated by them was provided. Unfortunately, this move in the right direction seems to have been accompanied ~~~
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1 Based on a paper presented before the Division of Chemical Education at the 132nd Meeting of the American Chemical Society, New Yark, September, 1957. ' BENEDETTI-PICHLER, A. A., FRANKSCHNEIDER, AND Omo F. STEINBACK, J . CHEM.EDUC., 34, 381 (1957).
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by a drastic redurtion of the number of laboratory hours. In addition, it does not seem to have been recognized that theoretical discussioos which are very valuable in selection and e~t~ablishment of methods, i.e., in analytical research, are of little use when praqticing proved procedures. They have no bearing upon the manipulative part of the work, and they provide no means for adjusting the effort to the required precision. With the small amount of laboratory time left, the effectiveness of the practical training thus came t,o depend mainly upon the ingenuity, resourcefulness, and endurance of the instructional staff. I t is here suggested that the discussion of theoretical considerations be supplemented with a thorough instruction in the details of basic laboratory operations. Emphasis should be placed upon development of the ability to recognize the operational parts of a procedure and to select intelligently those methods of performance for the various operational units that will assure final results of the required precision and accuracy. An intense effort for a relatively short time should give results far superior to those attainable with a laboratory instruction which leaves the student with the hazy comfort that he might be able to perform more diffidult assignments by a greater effort on his part, but with no definite ideas concerning the kind or direction of the effort to be made. The following two sections describe briefly how the proposed procedure of instruction may be put into practice by making the intelligent performance of unit operations the goal of the course. PROPOSED METHOD OF LABORATORY INSTRUCTION
The laboratory teaching is based upon individual use of a professional treatise on unit operations, which the student is to consult for all operational details of the experiments. The unit operations are presented in a systematic manner4 to aid the memory and to emphasize clearly the principles upon which they are based, the similarities, and the differences. Manipulations are described with the proper amount of detail; alternatives are given wherever desirable. Concise statements concerning limitations are supplied to permit intelligent a BENEDETTI-PICHLER, A. A., "Essentidls of Quantitative Analysis, An Introduction to the Basic Unit Operations," Ronald Press Co., New Yark, 1956. H A L ~ I TL. , T.,Anal. Ckhem., 29, 45A-47A (1957).
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selection. In general, the description of unit operations includes procedures for working with small amounts of material, centigrams (semimicro) and milligrams (micro). A collection of practice experiments is supplied in the form of an appendix and contains directions for all determinations customarily used in introductory courses. Alternatives are offered, and additional directions and suggestions suffice for two terms of advanced work. No distinction is made between inorganic and organic analysis since, with the emphasis upon general methodology, it would contribute nothing and raise an artificial harrier to general reasoning. The descriptions of the practice experiments are so brief that the student is forced to turn to the treatise of unit operations for information on procedural details. Even less advice is given with advanced experiments. Finally, the student is directed to try procedures found in analytical journals and in collections of official testing methods. I n nearly all instances, he is required t o base his reports upon findings that have been checked by multiple performance of the experiment. Insistence upon performance in duplicate and triplicate is deemed necessary for establishing the habit of repeated observation. I t produces several other benefits aside from developing efficiency. I t forces the student to organize his work and it prevents him from acquiring the habit of fiddling or fidgeting with one determination. The overly conscientious type is suhstantially aided hy not having time for useless worry and by the consolation that triplicate performance allows loss of one experiment. Multiple performance creates a professional air of purpose and urgency, and it frequently saves time hy eliminating the need for repetition of experiments. For the convenience of the instructor in organizing the course with the stock room, every laboratory assignment starts with a list of apparatus and reagents. This is supplemented by a brief description of t.he nat,ure of the sample for analysis. The statement of the principles upon which the determination is based is followed by reading assignments and problems that are closely connected with the experiments and furnish the information for an intelligent performance of the task. If text and laboratory assignments are announced in advance, interested students may save some valuable laboratory time by organizing the work at home. Naturally, a special effort must be made a t the start, when it is most essential to establish the habit of the proper method of study and the students have so many questions that the instructor is continuously tempted to interrupt the individual work by announcements. A quiz, assigned as home work a t the first meeting of the class, may serve for teaching the use of the text and for preventing some of the most disastrous mistakes frequently made in the laboratory. The author will supply the questions and other mimeographed information upon request. The laboratory assignments end by telling the student what to calculate and what to report. It is advisable not to accept reports that deviate from the directions and to post a schedule of dates on which specific reports are due. On the other hand, the students are materially aided by prompt checking of reports.
THE SECOND TERM COURSE
Enough work is scheduled for the introductory course to keep the most efficient and ambitious students busy. An advanced course is used to give the average student an opportunity to finish the basic assignments of the introductory course. In addition, all students are required to try the calibration of weights and volumetric apparatus. For the remainder of the laboratory time, the students a t Queens College are invited to select a menu according to individual preference. No administrative difficulties arise when the choice is limited to the experiments treated in the manual; using the lists of reagents and apparatus, the students can efficiently deal with a stock room that has been informed of the possible requirements. The calibrations are intentionally reserved for advanced work since they would take too much time in a beginners' course. As part of the first course, however, the reliability of weighing and measuring is demonstrated by simple experiments which also serve to provide exercise in these techniques. The method of the National Bureau of Standards for the calibration of weights is described. Its application to the calibration of one decade does not require much time and provides a unique experience that should not be missed in advanced training. Provided that the analytical balances are in good condition, determinations on the centigram or semimicro scale are possible with the use of tares and calibrated centigram weights. The assembling hy the students of a combustion train and performing of microdeterminations of carbon and hydrogen in simple organic compounds are within the range of possibilities and have been tried with success. ADVANTAGES OF THE PROPOSED METHOD
The proposed procedure of laboratory instruction gives a reasonable chance of attaining the teaching goal with the average student. I n addition, it has other features that should prove generally attractive. The instructor should tacitly assume the attitude of a director of research for the testing of analytical procedures. It is proper to conduct any science laboratory in the spirit of inquiry, and this trend is aided by the substitution of a professional manual for the customary school text. The interest, morale, and efficiency of the students will improve with the degree to which the illusion approaches reality. In addition to the students' favorable response, the instructor will obtain answers to the very intriguing problems that arise whenever new methods are tried or changes are made in established procedures. Aside from the need for supplying a brief but lucid outline of the theory of errors, the lecturer is free to proceed without particular concern about the progress of the laboratory work. He will try molding lecture and laboratory work into an entity since this aids the interest in both, but he need not adhere to a time table and he may feel free in the selection and treatment of topics. From the administrative point of view, it is desirable that the method of instruction have great flexibility. The order in which the experiments are performed may he changed and need not be the same for all students of JOURNAL OF CHEMICAL EDUCATION
a class. Performance in triplicate naturally causes a student to have six beakers on the steam bath a t one time or to need four Tirrill burners and tripods a t another. Instruction in the professional use and care of balances, volumetric apparatus, thermometers, and possibly calorimeters and spectrophotometers serves not only as an introduction to instrumentation, but will also meet with the approval of future employers and associates of the trainees. After 17 years, the inexpensive analytical balances used by the author's students are still suitable for semimicro work and the electric drying ovens are still practically new. Ambitious students find it possible to acquire a fair amount of experience in the introductory course. Various students have successfully carried out three gravimetric and seven titrimetric determinations in addition to the determination of three volume ratios and of the normality of six standard solutions. Because of the required multiple performance, this implies completion of about 50 to 60 individual experiments. SUITABILITY OF POSSIBLE ALTERNATIVES
I t cannot be denied that the personality of the teacher may be the most important single factor determining the impact of a subject upon a student. Under comparable conditions, however, it may be readily recognized that significant deviations from the proposed procedure must diminish the general effectiveness of laboratory instruction. Individual personal instruct.ion for the training of beginners requires one teacher for every three or four students. Personal instruction of larger groups is impractical. Aside from the fact that absences become a problem, the rate of progress must be adjusted to the slowest. Very soon, the instructor faces the alternative of either neglecting the slow members of the group or losing control over the majority who get bored and impatient. If conditions suggest it, group instruction may be used at the start, but it should not he continued for more than a few periods. Any form of written laboratory directions has the great advantage of permitting individual progress. Most convenient for fast work are directions that give all detail a t the point where it is needed. This means that all experiments must be described with inclusion of nll operational detail to permit changing the order of
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performance. I t also becomes necessary to reduce explanations to a minimum or to eliminate them entirely in order to keep the volume of the directions within reasonable bounds. Written instructions of this kind not ouly lack flexibility, but they are decidedly harmful since they invite thoughtless cooking and produce a confused medley of impressions which cannot be retained clearly since they are without order and system. Undesirable associations are formed, that connect, speciiic tasks to trifling details of manipulation and prevent the recognition of general principles. Supplying mauipulative detail in footnotes to the procedures may be an improvement, but the operational counseling still remains attached to particular procedures and cannot be given in a systematic manner and with the appropriate thoroughness. Flexibility may be attained by collecting the footnotes in a separate sedan or substituting for such a collectiou a dictionary of unit operations or an introductory chapter in which the needed operations are briefly described. All these devices, however, do not provide the desirable complete and systematic information needed for vocat,ional training. The customary sketchy treatment of the manipulative part stems from a refusal to recognize the inefficiency of personal instruction in large classes and may be harmful by creating the impression that "quantitative" results may be obtained without painstaking attention to detail. I t is felt that it is impossible to find a justification for a course in quantitative analysis that fails to emphasize the niceties of laboratory performance which are the distinctive feature of the subject. SUMMARY
I t is suggested that the effectiveness of laboratory instruction in quantitative analysis may be considerably improved by a shift of emphasis, while the customary selection of practice experiments may be retained. The suggested change may appear purely formal, but is actually quite radical. I t centers around the open acknowledgment that the foremost purpose of the quantitative laboratory is a training in the intelligent. and precise performance of unit operations, wherein the scheduled tasks assume the status of practice experiments. The student is taught the reasoning and the systematic procedure for a professional performance of laboratory tasks, and he should be able thereafter to apply this method to problems of increasing complexity.
