Teaching analytical chemistry. Need for objective ... - ACS Publications

SPECIAL REPORT

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TEACHING ANALYTICAL CHEMISTRY A Need for Objective Data

W.

E. HARRIS

Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada

APPROACHES to the teaching of analytical chemistry are continually being proposed and tried. Most of these ideas are likely to be successful in the hands of those proposing them because of the inherent attraction and challenge that analytical chemistry has for students and because of the interest and enthusiasm of the teacher. From the proponents of bold new schemes we are, therefore, likely to hear only positive reports. Nevertheless, some proposals are less sound than others, and in less committed hands they rnay be disastrous. An effort should be made to obtain comparative evaluations of boldly new, slightly innovative, and dyed-in-the-wool old approaches to teaching analytical chemistry. We should collectively gather as much objective data as possible as t o when, who, what, and how t o teach analytical chemistry. To obtain data of this kind on the broad questions of when analytical chemistry should be introduced, who should teach it, what should be taught, and even how it should be taught is admittedly difficult. Analytical

NEW

chemists should especially appreciate that greatest effectiveness requires defining objectives, analyzing effort, and acting according to findings. This is a report of some objective data gathered a t the University of Alberta. It is presented in the hope that others mill gathcr similar information that may help each of us arrive a t the most intelligent decisions for our own situation. Although addressed mainly to the academic analytical chemist, all chemists, industrial as well as academic, have a stake in the good teaching of all aspects of chemistry.

When Should Analytical Chemistry Be Introduced?

Objective comparative evidence as to the effectiveness of introducing analytical chemistry a t various times is especially difficult to obtain. Traditionally, the introductory course was in the second college year. Extended discussions have occurred about ways and means of teaching this course earlier or later in the curriculum. Beginning in 1962, six to eight

weeks of analytical chemistry wa4 introduced into the freshman general chemistry laboratory a t Alberta. The experiments chosen involved the use of unknown samples and included one gravimetric and two or three volumetric analyses. The hope was that the introductory parts of analytical cheniistry to follow could be ahbrcviated and possibly all the general chemistry laboratory eventually could be converted to analytical ivork. TT’e tried to do it right, including lecture-demonstrations and careful instruction of tenching assistants. Attempts were then made to obtain an objective assesment of the effectiveness of this instruction. [The question of the most suitable type of analytical experiments t o choose for instructional purposes is reluctantly approached here. Some praise thp use of unknown samples; others denounce them. The best ohjcct i r e evidence indicates that, with proper handling, experiments using unknown samples produce a much more positive response among students than seems achievable by other means (see Figure 4). It is sufficient now t o say that experi-

ANALYTICAL CHEMISTRY, VOL. 42, NO. 13, NOVEMBER 1970

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Special Report

Y

Freshmen

Instructed Freshmen

Analytical

Students

Analytical C.T.A.’s

Figure 1. Precision in buret reading by four groups with varying backgrounds

ments of the type shown to have high validity by the criteria described a t the end of this paper were used.] One small bit of assessment involved the minor item of reading a buret accurately. Four different groups of students were given a set of three burets with the written instructions: “Please read the burets as carefully as you can. Read the bottom of the meniscus.’’ The results are shown in Figure 1. The first group (freshmen) was a random selection of about 100 students registering in freshman general chemistry. The second (instructed freshmen) comprised a similar number who had been given some instruction (including how to read a buret) in analytical chemistry in their freshman year as described above and were now registering in the analytical course. The third group was the same as the second, but after two weeks of instruction in the regular analytical chemistry course. The fourth consisted of the analytical-chemistry graduate teaching assistants. The small relative difference between the first and second groups, if significant, may be owing to the greater selection of the second group or to the instruction received by them while they were freshmen. There is obviously an enormous difference between the second and third groups of students. The large relative difference between the third and fourth groups is significant to a high levcl of confidence and may be owing 54A

1962

1963

1964

1965

1966

1967

1968

Figure 2. The percentage of analytical chemistry students reporting superior results for two early experiments (chloride and glycol by titrimetry) and one later experiment (total salt by ion exchange and titration) during 1962-68

to either the more select fourth group or to their more extensive experience. The results of a second attempt at assessment are shown in Figure 2. The data are from results of the regular introductory analytical course for the seven-year period 1962 to 1968. I n the first year of this period the students came froin a general chemistry course that included no experiments in quantitative analysis. I n the years 1963 to 1965 about 30, 80, and 90% of the students had been exposed to analytical experiments in their freshman year. During this period the quality of work reported for typical early experiments in the analytical course (see chloride and glycol as examples) deteriorated. For typical later experiments there was little or no deterioration. Mainly as a result of the appearance of this unexpected trend, the inclusion of analytical experiments in freshman chemistry was largely discontinued. During the period 1966 to 1968 about 70, 20, and 10% of the students had been ex-


posed to analytical experiments in their freshman year. Coinciding with these decreasing proportions was a corresponding recovery of the performance of students in laboratory work in the subsequent analytical course to 1962 levels. During this period there was, unquestionably, a host of uncontrolled variables, and any interpretation can be questioned. Nevertheless, some conclusions seem justified. -4 third source of information was an anonymous survey of students registered in introductory analytical chemistry. The class, on the average, consisted of thirdyear students in a variety of fields, along with many second-year, fourth-year, and graduate students. S e a r the end of the year they were asked, among other things, to rate the course on a five-point scale ranging from highly unfavorable to highly favorable. Interestingly and probably significantly, the greateqt proportion of highly favorable ratings came from the fourth-year and graduate-student group.

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I n summary, though the buretreading item in itself can be judged validly to be rather trivial, it would seem to be of some value as an indication of attitude toward careful measurements. If this is accepted, then it is clear from Figure 1 that instruction in quantitative measurements as part of general chemistry siniply is not effective-it amounts to casual experience. Insistence on careful huret reading in freshman chemistry, for example, is likely to lead to a negative attitude about careful measurenients ; it is recognized t o tie a purposeless demand if other aspects of the laboratory do not meet the same standards. If analytical experience in the freshman year were helpful in the development of correct attitudes toward careful measurements, then a positive effect should be evident in courses that follow. The data of Figure 2 indicate that, contrary to expectations, analytical training in freshman general chemistry had a negative rather than a positive effect. Only after several months in the regular analytical laboratory did performance recover to normal levels, as indicated by the results of later experiments. K h e n the amount of analytical chemistry in the freshman labs was curtailed, the performance in the regular course in analytical chemistry improved. Teaching analytical chemistry as part of general chemistry appears unsatisfactory for several reasons : (1) The lectures and laboratory work usually are not well coordinated. Since freshman chemistry lectures tend to emphasize elementary physical chemistry, the background to laboratory work in analytical chemistry may be barely acknowledged. The lecturer may not be aware that he is deemphasizing the laboratory and may leave the impression that experimental work is not particularly important. Laboratory experiments are done in a sort of vacuum and can be called casual experience. 12) Supervision of large freshman laboratories requires a large nuinher of teaching assistants. Often this instructor pool contains the least experienced assistants and those unprepared for instructing

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in more senior courses. Their interest in and, probably, knowledge of sound analytical techniques may be marginal, and their nnderstanding of teaching techniques is often minimal. A combination of low interest in and knowledge of both the subject and how to teach results in dislike for analytical work. This situation is hardly conducive to either personal satisfaction or increased competence on the part of the student. (3) The time allowed for the laboratory is inadequate (normally three hours per week), only enough to expose a student t o some of the fundamentals, in some ways the least satisfying aspects of making chemical measurements. Experience shows that a series of appropriate lectures in conjunction with 100 to 150 hours of wellsupervised laboratory involving carefully selected experiments is required for a reasonable minimum of competence in .the basic experimental aspects of chemical measurements. (4) There is the danger, too, that an instructor mav think, "Analytical chemistry is 8. subject with experimental rigor, so we must insist on high standards," and uroceed to do so inconsistently. If high quality work is the goal, there must he no weak links in the chain. Critical pieces of equipment must he calibrated, chemicals and equip-

ment must be of adequate quality, and samples must be beyond reproach ( a difficult job). Instruction in how to get the most out of the laboratory, adequate esplanation of the chemical and physical background, and adequately motivated laboratory instructors are all essential. ( 5 ) Analytical chemistry is suited and appropriate t o only a small fraction of all freshmen. If rigorous experimental work is attempted where many are resistant to the attitudes and objectives being taught, the atmosphere is conducive to negative results. Analytical chemistry should he introduced somewhat late in a student's career and the timing should be flexible. A student should probe this subject when he has adequate background and motivation to appreciate experimental rigor and to understand why it is required. For chemistry majors a reasonable commitment t o chemistw -J probably taken place by thse second year, and therefore, they c:an take the course a t that time. Additional objective data on tllis topic .. would he especially appreciaGea. 1

What Should Be Taught in Analytical Chemistry?

The content of an analytical course, whether a t the introductory or advanced level, should bear au intelligent relation t o what goes on in modern chemistry laboratories.

The demand for analytical courses by students and staff will persist if the course is obviously fulfilling a useful purpose. If it is and remains out of date for any substantial period of time, it will wither. The effect of modernizing a course in analytical chemistry is illustrated by Figure 3. I n the 195960 session specific steps were taken to modernize the introductory analytical course a t Alberta and were pursued strenuously during the nest fivc years. Demand-. for the. course grew strimgly. Figure 3 compares growth rates in the introductory analy tical course with the enrollment gr,owth rates in the university as a whole. The growth ratc for enrollme,nt in the university and also the chemistry depart*"... ment was about ,owll,LI psL growth in the analytical conwe was about 40% per year. The biggest obstacle to modernization turned out to he this 40% growth rate when n ~ n n . inr cl O ~ I Vi- n- t,n ,,.-..I .". inrrea.apq ...".--l"-. l -15% had becn made. Some academic analytical chemists have had to adopt, out of neccssity, an attitude of defence. n ~ 1 / ~P I . . ' . ~ .-J oomc, as a resuifi 01 rc~iicab aiiu compromise, have shied away from treating their speciality as an honest discipline in its own right and attemptcd to develop laboratory exercises similar to those in physical chemistry. Physical chemistry laboratories are c-rtainlv imnnrX""

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56A

Adequate Good VeryGood Student Oplnlon of Lab

Outstanding

Figure 4. Student opinions of laboratory work in organic, physical, and analytical chemistry, and in other sciences (botany, genetics, mathematics, physics, zoology). Information from "Students' Union Course Guide," University of Alberta, 1968


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tant, but analytical chemists have something different to contribute. Some nonanalytical chemists have a notion that experimental work in analytical chemistry courses is basically boring, frustrating, and destructive to a continuing interest in chemistry. This impression is simply not correct; a well-organized analytical laboratory can stimulate students positively as no other laboratory experience can. The Students’ Council a t Alberta recently gathered data anonymously to evaluate student opinion about undergraduate courses, for publication in a course guide. This student-run project covered about 400 course sections in the faculties of Arts and Science. One item on the questionnaire asked, “How valuable did you find the laboratory for this course?” Figure 4 illustrates the response to this question for courses in organic, physical, and analytical chemistry along with an average for other sciences. I n general, the reaction to the laboratories for chemistry was more favorable than for the other scicnces. Analytical stands alone. The differences in student opinion for the various courses shown in the figure were not the result of significant differences in grading standards ; these were virtually the same for all four groups.

This question is of concern to all. One position is that it need not be taught as a separate discipline a t all, that is, that a series of casual experiences will do. It is difficult to see how deleting training in careful measurements in an experimeiital science can be an advantage. Even though the right material is taught a t the right time, the instructor will be ineffective if he is not committed to excellence in his subject. I n a laboratory, students are influenced by the attitudes of their instructors, their teaching assistants, the nonacademic staff, and their fellow students. If a significant fraction of any of these groups resists the point of view essential to an appreciation of the discipline, a student has difficulty becoming deeply involved. Primarily, however. he becomes involved in a sub-

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ject through the instructor’s deep commitment. Commitments are contagious. Better chemists will be produced if that part of their education dealing with chemical measurements is presented by a person who is expert and interested in analytically oriented research. Unfortunately, an analytical chemist too often is not available, and departments make do with someone not particularly interested in the subject. T o assign the teaching of any subject to persons whose principal interests are elsewhere is a major blunder. I n the first place, the person whose interests are not in analytical chemistry probably will not keep up to date with developments in this fast-moving field. He may well teach the same material he was exposed to in his undergraduate career and be 10 or 20 years behind. Moreover, he is unlikely to transmit the challenge and excitement inherent in analytical chemistry. The subject becomes horing and tedious, and everyone begins to cast around for a way out. Analytical chemistry taught under these conditions is both undefended and indefensible. When teaching it is regarded as an odious duty, the solution of integration may be seized upon, whereby responsibility for the subject becomes everyone’s and no one’s. While everyone should have some concern for reinforcement of the teaching of the several branches of chemistry, an interested group should have primary responsibility for each branch. Integration of organic, physical, or inorganic chemistry with any of the others probably would not do justice to any area. The same applies t o analytical chemistry. How Should Analytical Chemistry Be Taught?

Whatever it is that makes the mature chemist commit himself to work for long periods when nothing particularly exciting is happening cannot be expected to appear in a beginning student. But neither are the beginnings of dedication to a subject instilled by frant i c efforts to make it interesting through transparent gimmickry. For example, the “discovery method” of teaching often falls flat because, despite the effort expended

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in contriving situations to make a subject interesting, it is quickly recognized by the student to be unrealistic. Chemists generally perform two major functions: they gather information and they interpret it. The more soundly based their education in these aspects, the better chemists they are likely t o be. Any training that involves only casual experience with either of these two functions is bound to be weak. The learning experience in all branches of chemistry should be both rigorous and realistic; in analytical chemistry the primary aim should be to teach the student how t o acquire the knowledge needed t o solve problems. Undoubtedly there are many right methods of teaching analytical chemistry, each of them representative of an instructor deeply committed to his subject. Rather than attempt to give a n unsatisfactory and too brief summary of teaching techniques, a n objective method for evaluating instructional effectiveness is described. The method outlined can be used to provide a broad overview of a course or to examine a variety of detailed aspects. Evaluation of detailed aspects is an efficient way to bring into focus weak and strong points and thereby lead to the most productive use of instructional effort. None of us has to be an instructor for long before we know whether our teaching has been good or bad. A simple yes or no is easy. Of much more interest is whether the instruction is better or worse than last year-whether things are tending to improve or deteriorate. The strong and the weak points are not easily recognized by intuition. Every instructor calculates the average grade. The average, however, tells little about instructional effectiveness unless used with reference to some slippery absolute standard. But it is important in other ways. When it is low, students justifiably become discouraged and begin to say the instructor is unreasonable and unfair. When it is high, the course is called a "mickey-mouse" course, and the best students may feel cheated. Nonetheless, students recognize

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something for nothing, and the instructor may even become popular. An instructor can move a class average up or down a t will, and not necessarily in relation to instructional merit. If he wants to take an easy way out, or is faced with an uncomfortable situation, the assignment of high grades is a ready solution. Because the average grade depends on arbitrary decisions, it is of marginal value as a measure of instructional effectiveness. A more useful item for revealing trends in instructional effectiveness is discrimination. Briefly, discrimination is a measure of the difference between the performance of the best and the poorest students in a class for a test question, experiment, or other item. It correlates strongly with course effectiveness, student morale, and student attitude. A high value for discrimination is something an instructor has to earn; it depends not a t all on whim. Every incremental increase requires effort. (No claim to originality is made with respect to the use of the idea of discrimination; concepts of this type are widely used-for example, in the field of educational psychology. A system related to discrimination is used for validating ACS examinations. The writer has had personal experience with this concept for more than two decades. The student response exemplified by Figure 4 basically is a reflection of the innate appeal and challenge of analytical chemistry. It is also a result of having used discrimination as a device for selecting, polishing, and directing instructional effort over a period of years.) Discrimination can be calculated using two fractions of a class up to 50%. The numerical values obtained depend on the fractions used; for classes of moderate size calculations of discrimination a t the 20% level are preferred. To do this, the top and bottom 20% of a class are selected. A sound, convenient basis for making this selection is the overall final grade for each student. For each item to be rated the sum of all the marks obtained by the top 20% of the students and a similar sum for the bottom 20% are determined. Dis-

Special Report

crimination, follows : Dzo

(

- 2:bottom

Z t o p 20%

=

is calculated as

D20,

20%

zmaximum 20%

)

100

where Zmsximum 20% is the maximum marks obtainable on the item by 20% of the class. The class average is a relative measure of the difficulty of a question and should also be obtained for each item. A reliable average can be calculated from the same data used to obtain discrimination. Conveniently, average grade

=

Z t o p 20%

2

+

x b o t t o m 20%

zmnximum 20%

)

100

Example: Suppose t h a t in a class of 80 students a rating for a test item worth 5 marks is to be obtained. First select the 16 students (20% of 80) with the highest overall test grades and the 16 with the lowest. Then, on the 5-mark item in question obtain the sum of the marks by the top 16 students (suppose it is 6 5 ) . Similarly obtain the sum of the marks for the bottom 16 students (suppose it is 341. Then Dzo

=

65 34 16 X 5 ~

and average grade 65

+

x

100

=

39%

=

34

2X16X5

x

100 = 55%

The question remains as to what values for Dz0 and average grade to expect for various items in a n introductory analytical chemistry course and in particular for the laboratory. For the average grade, a value of about 60 to 70% seems reasonable, giving challenge mithout being unfairly harsh. T o furnish a broad overview of laboratory effectiveness. D20values for the experimental work as a whole are best. Over the last thirty years a t Alberta, using final course grades as a basis for selection of the top and bottom, D?o for the laboratory as a whole has ranged from a low of 11% to a high of 3 6 % . The average currently is 3 2 % . I n general, the value of discrimination depends partly on the nature of the experi-

mental work and partly on how efficiently it is supervised. With a Dzo value of 10% or less, teaching effectiveness is likely to be shockingly bad. At 10% the general effect of the grades assigned to the laboratory portion of a course will be to clobber the very best students, generally lon-er the grades of the good students, be about right for the middle students, generally raise the grades of poor students, and give massive bonuses t o the poorest students. Morale may be poor, and complaints are likely to be numerous. An overall value for Dz0 of about 20% for the experimental work can be considered adequate. The effects described above remain to a less demoralizing extent, but improvement is needed. At a D Z ovalue of 30% the operations are highly satisfying for both students and staff. (If a percentage grading scale is not used, obviously the values quoted here will be of marginal value. Alternate standards for acceptable discrimination will need to be developed by the reader for his particular grading scale. Discrimination a t other levels can be calculated; if classes are small Ds0 should be used for increased statistical validity. Djo ratings have lower values; a useful rule of thumb is that the D Z ovalue is about one half of the D Z ovalue for the same group. Thus a D:o of 5 % is poor, 10% is adequateland 15% is excellent.) There is strong positive correlation between competence in experimental work and that in the theoretical aspects. For example, the ten hest students during a recent period had vear averages of 97. 93, 92, 92, 91. 9U, 89, 89. 88. and 88Yo. Their laboratory grades were 100. 99, 88. 89, 92, 81, 89, 98. 88, and 92%. Similarly. the ten poorest students had year arerages of 18. 24, 31, 32, 33, 34, 34, 35. 35. and 35% and laboratory grades of 25. 29, 36, 45, 19, 44. 41, 37. 37, and 47% This kind of correlation tends t o prevail a t all leT-els of achievement when discrimination i q high. h high value for discrimination does not permit many weak points. Conditions have to be arranged so that good work is not only possible, but sought after. When the over-

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all value for discrimination for the experimental work is lower than desired, the items needing improvement should be identified. T o reveal the weakest links, Dz0 and average grade for every item in the laboratory are obtained first. When D z o for an item is in excess of 20%, no immediate attention is needed, but a t much less than 20% suitability or management should be questioned. When the average for an itern is either hich or low,

structor deeply committed to his subject and convinced of the correctness of his choices. No matter what approach is chosen, its effectiveness can be maximized through application of some method for objective scrutiny,

difficulty oT an itern and the generosity of the grading scale. The int,rodiict,inn nf new exneri-

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Introduced with enough polisb t o produce acceptable values for discrimination immediately. As an illustration, several years ago a simple and straightforward experiment was introduced which involved the determination of total salt in a sample by ion exchange and acidbase titration. The first year the DSnvalue was only 4%. Although nothing was fundamentally wrong with the experiment, several details were imoroved. The next Year the D,, v a i e was 16%. Again im-

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D2,the following year was 24%. For a third time the item was improved, and D 2 , for the fourth year was 34%. Discrimination for new experiments is often low because high-quality results cannot be expected until the directions have been refined. Initially, relaxation of the grading scale may be necessary to avoid an excessive number of poor grades. After polishing, reasonable grading standards can he met by a substantial fraction of the class. T o pinpoint the weaknesses, yearly calculation and comparison of D2, and average-grade values for individual items is worthwhile. With a knowledge of these values the contribution of each detailed item t o the realization of one's goals can be assessed. The best way to teach chemistry, and analytical chemistry in particular, surely has not yet been defined; furthermore, a single best way probably does not exist. 'Undoubtedly there are several right ways, each representative of an inUL R

f i i w L i I ILAL LntIv1151

nr,

VUL.

42, NO. 13, NOVEMBER 1970

Acknowledgment

The author acknowledges the assistance and interest of the members of the Analytical Division at the University of Alberta: W.

E. Harris is professor of

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sity o f Alberta, Canada. H e received his B S c . and M S c . from the University of Alberta and studied under Dr. I . M . Kolthofl at the University of Minnesota where he obtained his Ph.D. in 194.4. I n 1946 he joined the stafl of the Department of Chemistry at Alberta. His research has been in the fields of polarography, amperometric titrations, synthetic rubber, information retrieval, hot atom chemistry, and chromatography. For the past decade his eflorts have been principally in the field of programmed temperature gas ehromatography Dr. Harris is a Fellow of the Chemical Institute of Canada and coauthor or author of about 60 research papers and of "Programmed Temperature Gas Chromatography" (John Wiley, 1965) and "Chemical Analysis" (Barnes and Noble, 19Y0). I n 1969 he received the Fisher Award in Analytical Chemistry from the Chemical Institute of Canada.

Teaching analytical chemistry. Need for objective ... - ACS Publications

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