ELEMENTARY QUANTITATIVE ANALYSIS IN A SMALL LIBERAL ARTS COLLEGE HAROLD M. STATE Allegheny. College, Meadville, Pennsylvania
INORDER THAT the elementary quantitative course may be approached in its proper perspective, may I first outline our whole analytical program at Allegheny College. The sophomore chemistry major normally takes a two-semester course in qualitative analysis. This int,ensive course results in many of the weaker students changing their field of concentration and provides a smaller but more apt group for quantitative analysis which is ordmarily taken in the junior year. As a senior, the major may elect a course in "advanced" quantitative analysis. The premedical students and others not majoring in chemistry who do not wish to devote two years to analytical chemistry normally elect a year course comprised of one semester of qualitative and one of qnantkative. This separation of students on the basis of interests makes possible more intensive courses for chemi&ry majors. All of these courses have one lecture and two laboratory periods per week throughout the year. In the course for chemistry nlajors the first semester's laboratory work is devoted exclusively to gravimetric procedures. Water in a hydrate, chloride, sulfur, iron, and phosphorus in soluble salts, and a limestone are done in the order given. The titrimetric work of the second semester is begun with redox reactions, since it has been found that students have less difficult,y with these end points than with any of the others. Permanganate is employed to determine iron in an ore, the oxidizing power of pyrolusite, and calcium in the limestone begun in the first semester. Iodine is used for antimony in stibnite, and thiosulfate for copper in an ore. Fajan's chloride and a Volhard titration illustrate precipitation methods, and acid-base experience is given with the analysis of an acid and a soda ash. The year's work is concluded with the analysis of a brass, principally to give the student some experience with electrolytic methods. Throughout all the laboratory work emphasis is placed on the acquisition of good technique. The class periods are devoted to the theory of quant,itative analysis and to the solving of numerical problems. Since the student has encountered a thorough disrussion of ionization, hydrolysis, instability, and solubility product constants in qualitative these topics are covered rather hurriedly by way of review. Numerical problems are assigned the student to assist him in this review. The factors affecting both the completeness of precipitation and the purit,y of the precipitate, the choice of indicators, the applications of electrode potentials, the sources of error in each determination, and
other applications of the laboratory procedures are extensively treated. Early in the course an attempt is made to give the student an understanding and appreciation of the analytical balance a~ a fundamental laboratory tool and of the theory of measurement. Except for the usual reference to the law of probability no use of statistics is made in connection with the latter. The problems in stoichiometry are, by and large, selected so as to acquaint the student with analytical methods other than those he has actually employed in the laboratory. When the student has progressed far enough he is assigned problems in which he is asked to devise a suitable procedure for analyzing simple mixtures. The last two or three class periods are devoted to a brief discussion of some of the tnore important instrumental methods of analysis, although none of these is actually used in the laboratory. It is our feeling that every student of quantitative analysis should a t least know that there are other methods of analysis besides the ones he has used, when these methods are particularly advantageous, and what their limitations are. The principle of each method is also considered but time does not permit much detail. Instrumental determinations have not been included in the elementary laboratory work but do constitute an important part of the experimental work in the advanced course. Some may be surprised that no calibrations of either burets or weights have been included in the course. These have been omitted not because it is felt they are unimportant but because there isno more deadly way of killing a beginner's interest. Thwe procedures are also very time-consuming for beginners and result in much congestion and delay a t the balances. By providing apparatus of good quality, apparatus errors are not too serious. Calibrations are made a part of the advanced course. In the course for premedical students, less emphasis is given analytical theory. Accompanying the qualitative analysis in the first semester, ionization and solubility equilibria are considered in sufficient detail so that the student may have an understanding of the laboratory procedure. The calculation of pH values is emphasized. In the quantitative half of the course, titrimetric methods are stressed. Two gravimetric determinations- % of water in a hydrate and chlorideinitiate the laboratory work and give the student experience with the balance. Permanganate, iodine, thiosulfate, acid and alkali solutions are employed for one determination each. To conclude the experi-
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mental work two colorimetric d e t e h a t i o n s are done, one illustrating the use of a visual and the other of a photoelectric colorimeter. The acquisition of good laboratory technique is again stressed in the laboratory. The classwork is more concerned with the "how" than the "why" of quantitative analysis. Other appli-
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cations of the methods employed in the laboratory are discussed and illustrated with problems. Much practice is given in solving numerical problems, pH and buffers are reviewed again, and the selection of indicators is considered. Of the physicochemical methods only colorimetry is considered a t the present time.
