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THE CORRELATION OF THE GENERAL CHEMISTRY OF THE METALS WITH QUALITATIVE ANALYSIS GEO.W.SEARS. UNIVERSITYOa NEVADA, RENO, NEVADA Few teachers of first-year college chemistry would hold that the usual course in elementary qualitative analysis is expected to produce analysts. It is, however, well adapted to present, in a practical manner, certain fundamentals of chemistry. The average student who takes this course finds an interest in its systematic development, its practical application and its directness that holds his attention and creates a feeling that he is learning how to find out the very thing he had often wanted to know, vie., what things are made of. On the other hand, his study of the general chemistry of the metals with occurrence, preparation, and properties repeated with each new metal and each new compound is often uninteresting and, to him, disconnected and therefore fruitful of little more than the storing of unrelated facts most of which are forgotten soon after the final examination is over. Assuming that the aim of these two courses is to give the student a general knowledge of the chemistry of the metals, to prepare him for the more careful manipulation of qualitative analysis and to develop in him a certain ability to draw conclusions from facts, i. e., to enable him to use the scientific method of thinking, it is evident that the latter course, a t least, often falls short of its purpose. It was to correct this difficulty as well as to discourage the tendency on the part of many students to memorize facts without orienting them that prompted the writer, about four years ago, to attempt a correlation of these two subjects so as to give the general chemistry of the metals the benefit of the interest obviously created by the qualitative analysis. The result has been especially satisfactory and has demonstrated that the two subjects can be presented in complete harmony as a single course with an increased interest on the part of the student. He obtains a more systematic and logical idea of the metallic elements and is less inclined to memorize apparently unrelated facts without classifying them. Two fundamental generalizations form the basis of classification, &., the periodic table and the law of mass action. By means of these the student is able to understand the reasons, not only for his manipulations in qualitative analysis, but for the occurrence, preparation, and properties of the diierent metals and their compounds. Their use, therefore, is explained a t the very beginning of the course and the student soon learns to use them in a qualitative way. During the first semester's work on the chemistry of the non-metals the student has become somewhat familiar with the more common acid radicals and has found that double decomposition reactions are not only reversible but that the equilibrium produced may be shifted by the ad-
dition or removal of one of the substances concerned. He has also been given an idea of the periodic table and has seen its value in a few cases. He is, therefore, in a position to proceed a t once with the qualitative analysis of the acid ions while he is learning the use of the mass law as a means of explaining necessary procedures, and of the periodic table as a means of classifying the elements. Although many prefer to leave the acid analysis for the end of their course and direct the students' attention mainly toward the metals, much value can be obtained by a systematic stndy of the acid ions, their stability and relation to each other. It not only serves as a practical illustration of the relative stability and therefore usefulness of the diierent salts but brings to the student a clear realization of the meaning and effect of oxidation and reduction, two important chemical processes. It also serves as an excellent introduction to metal analysis since the reactions involved are comparatively simple. A laboratory study of the acid ions is well suited to the more general study of the alkali metals in lecture and recitation since the study of these metals is largely a study of their salts, many of which are of commercial importance because of the acid radical. The course, therefore, is best begun with a review of the periodic table and of its value in correlating the facts of chemistry, followed by an explanation of the mass law and its use in chemical manufacture. The student is thus prepared for a logical consideration of metals as differentiated from nonmetals and for the study of the alkali metals and their compounds. During this time he has completed the acid analysis in the laboratory. The metal analysis is then begun with a study of Group V, instead of Group I, as is often done when qualitative analysis is given as a separate course. It has been found, however, that this offers no handicap since it gives the student an opportunity to become acquainted with the methods of analysis before encountering the difficult theory and technic necessary for satisfactory work in Groups I1 and 111. In order to correlate the general chemistry of the metals wlth this order of analysis, the study of the alkali metals is followed by that of magnesium and the alkali earths and then by Division A metals,' continuing through manganese. The stndy of Group 111 analysis will have begun in the laboratory when aluminum is reached. Iron, cobalt, and nickel, therefore, should follow manganese. So far the lecture and laboratory work may be made to parallel as closely as is possible with students of varying abilities in laboratory skill. I t will be noted that this arrangement enables the lecture and recitation work to be presented in the most logical order when considered from the standpoint of the periodic table, the structure of the atom and the chemical conduct of the elements themselves. The most active and most basic metals as well as the most stable compounds are found in the See Periodic table by t t e author, THISJOURNAL, 1, 173 (Oct , 1924)
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study of the alkali metals. These properties become gradually less prominent as one proceeds with Division A metals through the different groups. Variable valence and the acidic character of elements also approach gradually. The student is, therefore, in a position to see the reason for the differences found in the occurrence, preparation, properties, and uses of the elements and compounds encountered. In order to continue this sequence, the study of copper, silver, and gold should follow that of iron, cobalt, and nickel and these should be followed by the other Division B metals in their regular order through the periodic table. With but one or two exceptions these metals belong to Groups I1 and I of the systematic analysis and hence can easily be made to parallel their laboratory study. A close relation is, therefore, obtained throughout the course between the systematic analysis and the apparently less orderly occurrence, preparation, properties, and uses. The interest developed by the former extends over the latter probably because the student is able to see the relation between the two and can hope to retain more of what he learns. Such a correlation possesses the value of introducing the more difficult concepts in a gradual manner. In acid analysis the student gets a practical working knowledge of double decomposition reactions with which he has already become acquainted. He encounters, however, instability in compounds as a property to be reckoned with. This shows him in a practical way that the methods used in the manufacture and use of substances, as well as in their analysis, must be governed by the character of the compounds concerned. He finds amphoterism in aluminum and sees how it is used and why i t exists and, therefore, looks for i t in chromium. He encounters variable valence and, therefore, oxidation-reduction in the study of chromium and manganese and a t the same time sees how it is used to advantage in the separation and detection of these elements. He comes to the study of iron, cobalt, and nickel, the transition group, by very gradual changes in the properties of the elements. He can, therefore, see the relation existing between the elements and can get a basis for correlating his facts and for drawing reasonable conclusions. The transition character of Group VIII prepares him for the great dserence he will find between the alkali metals and copper, silver, and gold and so tends to keep his faith in the periodic table as a means of correlating the facts of chemistry. The complex ion as a practical problem and as a useful agent is met in connection with Division B metals and so appears late in the course. All of these concepts appear naturally as laboratory problems. The student can readily see the need for their explanation since they have a direct bearing on practical analysis as well as on the chemical manufacturing industry. Instead, therefore, of becoming additional tasks for him to perform they appear as useful tools in his analysis and as explanations for the facts he has obtained.
