TEACH ANALYSIS FREDERICK C. STRONG 111 Stevens Institute of Technology, Hoboken, New Jersey
title of this paper states a point of view with which not every teacher will agree a t the present time. However, to the author, it seems the only way out of a sad situation, namely the declining status of the qualitative analysis course. As evidence for this description of its status, the following typical comments are cited:
THE
( I ) Ez-student: "Of little practical value in graduate research and industry; cookbook chemistry, stink chemistry." ( 2 ) Administrator: "Apparently not very importsnt. Let's reduce the hours or put it into the general chemistry course."
A more complete and more objective statement of this situation, its probable causes, and some possible remedies will be attempted through answering the following questions: Do the analytical procedures taught in most current qualitative analysis courses have real practical value? Most teachers familiar with industrial practice will agree that the answer to this question is "no." However, an objective answer was desired by the author. Three well-known consulting analytical laboratories, whose work can be considered representative of typical analytical problems, were visited and queried concerning the use they make of the methods of qualitative analysis taught in the conventional college course. Their answers are shown in Table 1. I n interpreting the table, it is an important fact that the first two companies own spectrographs, while Foster D. Snell, Inc., does not, its spectrographic work being sent out. The author submits that the failure of the course to 1 Presented as part of the Symposium on Qualitative Andysis-What, Why, How?-before the Division of Chemical Education a t the 130th Meeting of the American Chemical Society, Atlantic City, September, 1956.
keep up-to-date, as showu in this table, is the reason for its decline.
sir
TABLE 1 Extent and Use of Methods Taught i n t h e Conventional Qualitative Analysis Course
United States Testing Co . Types of samples All Idnds received Uso of H9S uro... eednrcs Use of anion pro- Extensive cedures IJse of cation snot Moderate
- .
Lucius Pitkin, Inc.
Foslef. D. Snell, Zne.
Alloys, ores, concentrates
Coml. prepns.. detergents Occasional
Moderatc
Extensive
... . .
Ocoasional
W h y do many qualitatiuc analysis texts attempt to teach three subjects: analysis, physieal chemistry, and descriptive chemistry P Authors of many popular qualitative texts have no hesitation in stating that their primary purpose is to teach physico-chemical principles and descriptive inorganic chemistry. I n the face of the decline of the prestige of the course, this must be interpreted as an attempt to justify retaining it in the curriculum. When the latter contains bona fide courses in physical chemistry and inorganic chemistry, the fallacy of this approach is obvious. I s qualitative analysis a n important branch of analytical chemistry? The three companies previously cited all agreed that many of the samples they receive require qualitative examination. The growth of the practice of qualitative analysis has paralleled that of quantitative. En-
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tirely new and much more sensitive methods have been developed. Their importance to industry cannot be overemphasized. It is desirable that students of chemistry, engineering, metallurgy, medicine, etc., be aware of these methods and have some understanding of their principles. If possible, they should have first-hand experience with them in the laboratory. What methods of qualitative analysis are used currently in i d u s t r y ? This question was put to the three consulting laboratories named previously. (See Table 2.) Summarizing their answers, arc-spark emission and anion tests are used extensively; X-ray diffraction, microscopy and X-ray fluorescence are used moderately, and cation spot tests are used occasionally to moderately. TABLE 2 Extent of Use of Methods of Analysis United States Testing Co.
Lueim Pitlein. Ine.
Metals a d cations Arc-spark emission Extensive Extensive Spot tests Moderate X-ray fluorescence . .. EX&& Anim Systematic 61 direct t e ~ t s Extensive Moderate
Foster D. Snell, In&.
Extensive Occasional Occasional Extensive
Compounds
X-ray diiraction Microscopy
Moderate Occasional Moderate Moderate
( 5 ) The importance of microscopy, X-ray diffraction, and density implies the value of giving the students an elementary grounding in crystallography. The principles of these methods should also be explained briefly. While advocating analysis as the theme of the course might seem to imply suggesting a purely practical course, this would be indefensible. The college curriculum is not designed t o turn out technicians. Even though students enter the course with some background in chemistry and physics, the principles that are of value in analysis require restatement and amplification. However, if new material is to be added, theory not essential to an understanding of qualitative analysis has to be rigorously excluded.
A final questia may be asked: What modern methods of qualitative analysis is it feasible to teach in the laboratory to large groups of students? A description of the author's experience with the type of course proposed will offer some answers t o this qnestion. Spectroscopic methods are the most important addition to make. Spectrometers can be purchased from a number of suppliersz for less than the cost of a good analytical balance. If the budget is short, as is often the case, and relations with the physics department are good, which is usually the case, the latter can be counted on as a source. An illuminated scale is to
Moderate Occasional
Miscellaneous methods used, but not listed in the tables because the applications are generally in quantitative procedures, are: Ion exchange, paper and column chromatography (in organic separations) and, occasionally, polarography. The value of experience in drawing initial couclusions from sample origin, appearance, and density was stressed by the persons interviewed. A revealing fact discovered during discussions is the difficulty of completely dissociating qualitative and quantitative analysis in practical work. Industrial analysts generally perform their qualitative tests in such a way as to give semiquantitative estimates. Smce a purely qualitative test is not of great value, this suggests that we should be teaching semiquantitative estimation in the qualitative course. DESIGNING A MODERN QUALITATIVE ANALYSIS
COURSE
If the results of this study are to be used as a guide in formulating a course syllabus, certain conclusions are inescapable: (1) Current teaching of anion identification methods is satisfactory and should not be neglected in favor of cation methods. (2) While brief mention of the systematic separation and identification of cations can be retained in the lecture part of the course, the time devoted to it in the laboratory can be much more profitably spent on other methods. This does not mean the elimination of fractional precipitation. It is used in some cation spot tests and in many anion procedures. (3) The theory of arc-spark, flame and fluorescence emission should be added to lectures. (4) Because of its high rating, emission spectroscopy of some sort should be introduced in the laboratory. VOLUME
34,
NO. 8, AUGUST,
1957
be preferred over cross-hairs for visibility. Flame tests are an obvious place to begin. Here, the transient nature of the emission from a drop of solution on a platinum wire loop has been a deterrent to spectroscopy. A successful technique is illustrated in the figure. The sample (1-2 ml.) is placed in a plastic hand atomizer (available in most drug stores) and atomized into the opening in the side of an earthenware flame guard. Operation of the atomizer for a few seconds fills the interior of the flame guard with spray, causing a persistent emission that is easily read in the spectrometer. The small number of lines produced in a low-temperature flame permits the use of a simple Baumh and Lomb Optical Company, Rochester 2, New York; Americsn Optied Company, Buffalo 15, New York; Central Scientific Company, Chicago 13, Illinois; Ealing Corporation, Natick, Massar.husntta.
spectrometer with limited dispersion. In laboratories with a compressed air line on the desks, it would undoubtedly be possible t o construct an arrangement utilizing an atomizer of the type used in flame spectrophotometers. Visual arc-spark spectroscopy can be carried out using the "Fisher-Todd Spectranal" or similar homemade apparatus. The method consists of sparking a wire sample in a 1.6 M HN08 solution or dissolving the sample in such a solution and sparking between platinum electrodes. The wire a t which sparking is desired is immersed t o a depth of not more than 1-2 mm. in order to have high current density. The other electrode is extended deeper into the solution. Because of the low voltage used (90-120 volts) and quenching by the liquid, only a small number of lines are produced, and visual observation is quite satisfactory if the mixtures are not too complex and if the student realizes that several lines are required to positively identify an element. It is most satisfactory to use con~mercialalloys as cation unknowns, rather than solutions. Companies such as the Allegheny-Ludlum Steel Company, the International Nickel Company, the Aluminum Company of America, and the Dow Chemical Company are very generous with samples of their alloys. If obtainable, fabricated alloy specimens make the most interesting unknowns. Systematic cation separation by HB or other reagents is replaced in the course by spectroscopic methods and spot tests, but the latter have no advantage over systematic testing unless the student is taught t o make some intelligent guesses concerning probable composition. I n the case of alloys, tests with a magnet, estimation of density, and observation of the presence or absence or characteristic corrosion products are used to provide a basis for a preliminary guess that is verified with a spot test. Aft,er identification of the principal metal, the metals commonly alloyed with it are tested for. Spot tests need not employ exotic, unobtainable reagents. For example, metallic aluminum is readily identified by hydrogen evolution when
treated with 6 M NaOH, while small amounts of magnesium can be detected by the coloration of magnesium hydroxide with adsorbed iodine. Inclusion of experiments in other methods must depend on the amount of time available. For example: Disc paper chromatography can be performed easily in a petri dish.3 A procedure for removing interfering cations with a cation exchange resin prior to anion analysis should not be difficult to devise. Subjects that must he limited because of time and equipment can be made special projects and divided up among the class during one or two spare periods. Ultraviolet induced fluorescence can illustrate the principle of X-ray fluorescence as well as serve as a test for identifying al~minum.~ A source of ultraviolet radiation and a viewing box are required. A spectrometer would be an optional addition. Visual absorption spectroscopy is not of much use in qualitative inorganic analysis, since permanganate ion is the only common ion with maxima in the visible range. However, its extensive applications in photoelectric (rather than visual) form in qualitative organic analysis and quantitative inorganic analysis would justify a brief visual experiment or demonstration. A homemade triangular cell (to vary the solution thickness) can be inserted between a strong source of white light and a spectrometer to show the absorption bands of permanganate ion. ACKNOWLEDGMENT
The author wishes to acknowledge the cooperation and assistance of Chester A. Snell and B. S. Van Zile of Foster D. Snell, Inc., Robert H. Bell and Charles A. Jedlicka of Lucius Pitkin, Inc., and Robert C. Putnam; Raymond D. Dewey and John H. Allwein6 of United States Testing Company. "URAK,
J. G . , AND R. J. MARTINOYICA, J. CAEM.EDUC., 32
95 (1955).
WHITE,C. E., I d . En& Chem., Anal. Ed., 18, 530 (1946). Present address: E. F. Drew Company, Boonton, New Jersey. Present address: Chase Bras8 Company, Waterbury Connecticut. 4
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