OBJECTIVES IN THE TEACHING OF QUALITATIVE ANALYSIS* J SAMUEL GUY,EMORY UNIVERSITY, EMORY UNIVERSITY, GEORGIA
The last few years have witnessed an interesting change in the teaching of inorganic chemistry. Textbooks dealing with this subject were formerly filled to a large extent with descriptive material; more modern books are containing less description and more of the principles of chemistry. This should be a very welcome change. Chapters on colloids, electrochemistry, equilibrium, etc., are rapidly crowding out of the elementary inorganic text much of the information formerly given there in connection with the study of metals. For example, in a modern book a chapter on lead would deal more with the use of lead in the storage battery than i t would with the properties of many of its compounds. In a similar way hard water, lime, cement, and plaster of Paris become interesting topics in the discussion of calcium. There is usually very little connection between the laboratory work and the recitation in the part of the introductory course in which the metals are discussed. Many excellent teachers have adopted an elementary course in qualitative analysis to accompany the last few months of the work in inorganic chemistry. It is my opinion that this is a good thing for the student who takes only one year of chemistry, but does the student himself feel the relation of what he is studying in the text to what he is doing in the laboratory? While this change is going on in the teaching of inorganic chemistry changes of equal significance are also coming about in qualitative analysis. In the teaching of this subject we may say that there are three distinct types of courses being given. In the first place, a course in qualitative analysis may be true to its name and have as its definite object the analysis from a qualitative standpoint of a large number of substances. In such a course there is generally very little recitation or lecture work. The student goes about his work with one thought in mind and that is the development of technic in the various procedures whereby he will be enabled to separate and identify the metals and their corresponding acid radicals. The success of such a course is generally measured in the "number of unknowns" that a student has satisfactorily solved and in the many different and difficult separations involving silicate fnsings, separation of incompatible substances, etc., which he has made. This type of course finds very little place in the modern college curriculum; schools of mining, engineering, etc., still haxe it as a necessary part of their instruction. A second objective in the teaching of qualitative analysis is to use it as a
* A paper read before the Division of Chemical Education of the American Chemical Society at Detroit, Mich., September 7, 1927.
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training ground for the writing and balancing of chemical reactions. Where this type of course is given, the student is expected to take, for example, a test solution of silver nitrate and treat portions of it with a long list of reagents, obtain a precipitate, dissolve the precipitate, as the case may be, and immediately write all reactions involved. In my own mind I can see standing before me, like Banquo's ghost, a t least a dozen test tubes, suitably supported in a test-tube rack, in each of which a 5 cc. portionlof silver nitrate had been treated, respectively, with hydrochloric acid, hydrogen sulfide, potassium chromate, ammonium hydroxide, and many other reagents. And before me lies a solid page of neatly balanced chemical equations illustrating, probably, via graphite, just what has happened in the test tubes. Personally, I am opposed to such a course as i t does little more than spoil the student's appetite in the field of chemistry. I believe that any professor is guilty of criminal negligence when he side-tracks the fundamental principles of chemistry for the sake of balancing on paper a number of chemical reactions. However important one may think this large number of reactions to be, the fact still remains that only those actually involved in the separation and detection of the metal concerned should be remembered by the student; further, he retains the facts better if he be permitted to follow only the particular ion in question without much emphasis on such other companions as may be in the solution with it. Finally, as a third objective, the subject of qualitative analysis may offer an excellent place to bring home to the student many of the fundamental principles of chemistry as they are exemplified by the behavior of the metals. A course of this type is fundamentally based on full appreciation of the theory of electrolytic dissociation and law of mass action. Stieglitz of Chicago and Noyes a t Boston Tech. have been to a large extent responsible for this innovation in the teaching of qualitative analysis. We owe them a debt of gratitude for their excellent work and texts which have so influenced modern analytical chemistry. Place before the student a table of solubility products of barium, strontium, calcium, and he will with very little assistance arrange a scheme for their separation. Teach him the solubility product theory fully, explain to him the effect of a common ion and he will understand how it is possible to separate groups I1 and I11 even though they both are precipitated with hydrogen sulfide. See that he understands why the presence of ammonium chloride prevents the precipitation of magnesium hydroxide by ammonium hydroxide. It is far better, in my opinion, for him to know this principle than it is to be able to write the reaction involved, and far easier and more interesting. The amphoteric nature of elements is beautifully illustrated in the separation and detection of zinc, aluminum, and chromium. Their behavior is almost human and I've never found the
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slightest difficulty in getting a "rise" out of the student in the study of this group. To this end I believe that a course in qualitative analysis should not be predominately laboratory work but should be accompanied by a liberal number of lectures and recitations, not less than two or three recitations per week. It is well for a student to know definitely the object of his work before he begins it. Therefore, laboratory work should consist of definite experiments arranged to illustrate definite principles and fundamentals and not a hodge-podge of schemes memorized and unknowns solved.
