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AN UNDERGRADUATE COURSE IN SPECIAL METHODS OF ANALYSIS GALEN W. EWING Union College, Schenectady, New York
THE great and steadily increasing importance of instrumental methods in routine and research analytical chemistry makes it a matter of prime importance that students majoring in chemistry be given some familiarity with these techniques. To this end we have introduced a t Union College a course called "Advanced Analytical Chemistry" which runs for a full year with one lecture-recitation and one three-hour laboratory each week. This course is normally taken in the junior year. The students in our technical course, leading to the degree of B.S. in Chemistry, have already taken full-year courses in classical quantitative analysis and organic chemistry, and are taking physical chemistry. On the other hand the less technical chemistry "majon" have had only a year course in quantitative analysis with half the amount of laboratory work, and are currently taking organic; for them physical comes in the senior year. Hence the advanced analysis class is rather heterogeneous. The result of this situation is that all of the necessary principles of physical chemistry must be developed as we go, or in some instances taken on faith. The first several weeks of lecture are devoted to methods of locating the equivalence point in volumetric titrations. After a resume? of simple indicator methods, conductimetric titrations are discussed, followed by potentiometric analyses. The latter subject is presented from the viewpoint of the Nernst equation, but it is considered beyond the scope of this course to derive it. An important point which seems difficult for many students is the difference between a potentiometric analysis for a free ion on the one hand, and for the total potentially available ion on the other. The former can be completed with only a single setting of the potentiometer, as in the determination of pH with a glass electrode, while the latter requires a lengthy potentiometric titration. The study of potentiometry leads conveniently into polarographic analysis. The theory of this instrument need only be carried far enough to show in a qualitative way why it works as it does. For purely analytical purposes the polarograph is most conveniently used in a relative way, in which the curve obtained for the unknown is compared with a family of curves determined under the same conditions for standard solutions. Hence the IlkoviE equation need not be employed in the calculations. This equation is therefore only mentioned in order to show that the theory does have a sound mathematical basis. The next major topic is the absorption of light. This
is developed from the Beer-Lambert Law, with applications to the several types of photometric apparatusNessler tubes, variable depth colorimeters, photoelectric filter photometers;and spectrophotometers. The theory of chromophores is passed over briefly, but emphasis is placed on the development of colors by reagents. This discussion is extended beyond the visible region into both the ultraviolet and infrared spectra. The classical spectrographic techniques are dealt with in some detail. Rather than describe numerous alternative procedures, we fix our attention on one or two of them for which we have illustrative material available. I t is felt that no useful purpose would be served by giving great detail about homologous pairs, internal standards, and the like. The identification of lines by comparison with an iron arc spectrum and reference to tables, coupled with quantitative determinations based on a logarithmic rotating sector are readily understood, and give sufficient insight into the essentials of spectrographic work. The lectures for the rest of the year are devoted to a sequence of more or less unrelated topics, including radioactive tracers, ion-exchange, chromatography, and various principles of gas analysis. Many of the topics considered in detail in the lectures and text are not available to us for laboratory experiments due to budget limitations. In place of them we include a number of experiments which illustrate principles already known to the students but not assigned as experiments in other courses. We have lifted from our physical chemistry course several experiments previously performed there which are primarily analytical. This in turn permits the inclusion in the physical laboratory of more experiments designed to test basic theory. The experiments a t present assigned in the advanced analytical laboratory are: 1. Determination of nitrogen by the Kjeldahl method. The semimicro apparatus of the Hengar Company is used. 2. Determination of carbon dioxide in limestone bv absorption of the evolved gas absokp- in a weighed tion tube. 3. Spot tests, using Yagoda Confined Spot Test Papers (C. Schleicher and Schiill Co.). Copper is estimated by dithiooxamide. 4. Determination of total cations in solution by ion-exchange. 5. Determination of fat in foodstuffs by Soxhlet extraction. '7
JOURNAL OF CHEMICAL EDUCATION 6. Electrodeposition of copper (for those students who have not previously performed the equivalent experiment elsewhere). 7. Determination of sucrose in a syrup with a polarimeter. 8. Determination of the hardness of water by titration with disodinm dihydrogenethylenediaminetetraacetate ("Versene").' 9. Couductimetric titrations. The solubility of silver sulfate is determined by titration with barium chloride. 10. Potentiometric titration of phosphoric acid with a Beckman glass electrode pH-meter. 11. Potentiometric titration of iodine by thiosulfate, and vice versa, using platinum-calomel and platinum-tungsten electrode pairs with a Fisher Junior Titrimeter. 12. Polarographic determination of mixtures of nickel and zinc in ammonium hydroxide-ammonium chloride buffer as supporting electrolyte. 13. Colorimetric analysis of nickel with dimethyl glyoxime, using a Klett-Summerson photoelectric colorimeter. 14. Spectrophotometric study of an indicator in a series of buffer solutions. 15. Chemical microscopy. A student-type microscope fitted with Polaroid in the eyepiece and below the stage is used to observe qualitatively the differences between crystals of various substances. A few representative precipitation reactions are observed directly through the microscope. 16. Chromatographic separation of the pigments from any convenient plant source.
' Cf. Chm. Eng. N m s , 27, 3658 (Deo. 5, 1949).
17. Analysis of city iuuminating gas by a combination of the standard Orsat apparatus with a "GowMac" thermal conductivity unit (Gow-Mac Instrument Co., Newark, N. J.). Carbon dioxide and monoxide are determined by absorption in the Orsat apparatus, hydrogen by oxidation with hot copper oxide, and hydrocarbons as methane by observation of the thermal conductivity of the remaining gas. Nitrogen is determined by difference. A calibration curve has previously been prepared for the thermal conductivity unit with known mixtures of methane and nitrogen. 18. An Emerson bomb calorimeter is used to determine the heat of combustion of a sample of solid fuel or foodstuff. Some of these experiments are planned to cover two consecutive laboratory periods, and some to be performed by a team of two students. The experiments are staggered so that each student can do aU of them in the course of the year. In addition to the formal experiments, the students are given a two-hour demonstration and lecture in the spectrographic laboratory of the General Electric Company, whose cooperation it is a pleasure to acknowledge. A number of important tools which belong in this field are omitted altogether, as it is felt that they cannot be treated adequately in the time a t our disposal. Thus the students must rely on the physical chemistry course for discussion of the mass spectrograph, X-ray, and electron diffraction. Throughout the course emphasis is on pointing out the possibilities inherent in the various analytical methods, rather than providing a working knowledge of specific procedures. The interrelationship of physical and analytical chemistry thus becomes obvious.
