A BEGINNING COURSE BASED ON THE PRINCIPLES OF CHEMISTRY ERNEST E. BAYLES, UNIVERSITYOF KANSAS, LAWRENCE, KANSAS New ways of doing things, if they are better ways, are in constant demand. Oftentimes, however, new ways are demanded whether they are better or not. There is a rather insistent demand for revision of the high-school chemistry course, possibly for the latter reason, but more probably for the former. In this article is presented the outline of a high-school chemistry course which is decidedly different from the one usually offered, and which, it is hoped, is somewhat of an improvement. Before organizmg any course, those concerned must f i s t have a clear realization of the end or purpose which the course is to achieve. The principal pnrpose of the high school has been variously defined as preparation of the citizen; that is, preparation of the average man, or of the layman. This individual, outside of his own vocational preparation, requires a generalized notion of the basic, governing principles which underlie the various aspects of his environment. He must be introduced to these principles, and that thoroughly enough that he will recognize and apply them when occasion demands. The course must be designed to give him probably the only systematic view of the science of chemistry that he will obtain. It may, of course, enlist his interest and lead him to follow up chemistry as a vocation, but m most cases it will not. The course must be adapted primarily to the studeflt who will not go farther into the subject. This type of student needs a course that will do two things. He needs first a "speaking acquaintance" with the common, every-day facts, ideas, and nomenclature of the subject in order to become conversationally intelligent regarding it. This will enable him to take an active part in discussions with his fellows and to read intelligently on matters dealing with chemistry. He needs, in the second place, to be able to apply the principles in the solution of everyday problems as they appear. New problems are always arising. The uninitiated is a t a total loss in facing them, but not so the one who can classify the problem and from this classification can deduce the solution. It is the primary purpose of the high-school chemistry course to establish a familiarity with things chemical, and a comprehension of the governing laws and principles. Not only the proper pnrpose of the course, but also the proper method of accomplishiig this purpose must be realized by the ones who make the course. If principles are to be understood, the course must be organized around these principles. The principles of chemistry, not the facts of chemistry, must determine the topics around which the discussions must revolve. Two questions immediately present themselves. First, what 1317
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shall be the order in which these principles are presented? Second, what shall be the method of presentation' The modern newspaper reporter recognizes the need of the busy man for getting the greatest amount of information regarding daily happenings in the least possible time. This is efficiency as demanded today. The first paragraph of each article embodies the essential points that are presented in the entire article. The later paragraphs are an elaboration of the first. They go farther and farther into detail. This same principle of organization should he followed in the beginner's course in chemistry. The first unit should cover the field, and each subsequent one should serve to elaborate, in greater and greater detail, the first. The order of topics in the course must be from the more generalized to the more specialized. The first unit in the following course is entitled "The Nature of Chemical Changes," but each and every subsequent unit also deals broadly with this same topic, the only difference being that special features are singled out for more detailed study as the course proceeds. The internal organization of each unit must embody the inductive approach and the deductive departure. This is the way man first discovered these laws, and it is the most effective way to teach them. Seemingly unrelated phenomena are brought to the student's attention and his interest enlisted in making an explanation which makes clear the relationship. Comprehension comes with the realization and verbal formulation of this relationship, and the test for cbmprehension is secured through the application of the principle to the solutioa of novel problems which involve the relationship. Thus, it is seen that chemical facts are needed in the course, hut as means rather than as ends. Any group of facts which serves to illustrate the relationship under consideration will be satisfactory. Those facts which statistical investigations show are most likely to reappear in the future experiences of the learner should he the ones most commonly used, but they are not the only ones that could be used. The relationships are essential, the facts are incidental. The following outlines present approximately two-thirds of a course in high-school chemistry in which an attempt has been made to follow out the above ideas in course organization. The basic principles of the subject are the unifying factor. They are taken up one a t a time and the student is expected to master each one before he proceeds to the next. Outlines are only partially satisfactory as a means of showing a method of organization. The reader must use his imagination in filling in the gaps and noting how one topic leads into the next. Each major division of the course is devoted to one of the major principles of chemistry, and is designated by the term "unit." No attempt is made to present to the student systematically a detailed list of chemical and physical properties of the various elements and their
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compounds. I n an incidental way he will become acquainted with many of these in the course of the year's work. In teaching the course, the attempt is continually made to bring the student into direct contact with as many substances as possible so that he will have the "feel" of them, and will know them through contact rather than through description. Experiments should be selected solely on the basis of their effectiveness in illustrating the working-out of the principle under discussion. The course has been used in high-school classes with a number of different teachers, and has shown itself to be practical and teachable. I t leads the student to see chemistry as the science of the behavior of substances, the comprehension of which will develop t o him the ability to foretell what this behavior will be. It will lead him to make his own activities intelligent rather than of the trial and error sort. The essential end of science is the prediction of behavior. This should be the primary end that the chemistry teacher seeks to achieve. Unit I. The Nature of Chemical Change 1. How to distinguish belwem chemical and physical changes. Gleaned from the observation of chemical and physical changes in the home and in the laboratory. 2. Horn chemical changer ad i n accordance with certain lams; such as the Law of Conservation of Mass, and of Definite Proportions. 3. How one n a y distinguish between the simple types of chcmical change: union, decomposition, and displacement. 4. How molecules are related to chemical chakae. Atomic and molecular structure. Significance. C Unit II. The Nature of Solutions 1. How true solutions differ from true suspensions. As to settling out, diffusion. changes in boiling and freezing points, osmosis, filtration, saturation phenomena. Practical applications. 2. The intermediate m t u m of colloidal conditions. Comparisons on the basis of the six above phenomena. Brownian movement. Color changes. Sols and gels. Protective colloidal action. Dimensional relationships between solutes, colloids. and true suspensions. 3 . How dissolved substances are recovered from solution. Precipitation method and the softening of water. Distillation and fractional distillation. Evaporation and formation of crystals. Crystalloid vs. colloid. Relative solubility and formation of crystals. Hydrated crystals. Efflorescence and deliquescence. Fractional crystallization. 4. Characteristics of solutions having solvents other than water. Unit 111. What the Chemical Ponnula Represents 1. Qzralitetiue representation of structure i n the symbols of .chemistry. Dalton's assumptions. Qualitative meaning of symbols in formulas. Derivation of symbols. 2. Quantitative representation of structure i n the symbols of chemistry. Molecular and atomic weights. Relative weights of molecules and atoms. Computations from the formula. The G. M. V. and Avogadro's hypothesis. Changes in boiling point and freezing ~ o i n in t relation t o molecular weights. Reason for this relationship. Volu-
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metric and gravimetric relationships and Gay-Lussac's law. Exponents and coefficients. Radicals. Representation of water of nystallization. Problems. Percentage compasition from the formula. 3. How formulas are derived from experimenfal data. From percentage composition, or from experimental weights. Find fractional part of each atomic w e -i ~ h t represented and express in the smalLwhale-number relationship. Verify the formula by comparison with the expe"menta1 molecular weight. Elements in the free condition. 4. How the simplestformula i s devived from the n a m of the substance. Multiple proportions and valence. Positive and negative elements and radicals. The use of valence in formula writing. Unit N. How Chemical Changes Are Represented
1. Eouations and chemical change. and arrows. Relation . Meaning - of pluses . between word-equations and formula-equations. 2. How the eountion regresents w&ht relationshigs. The balancing of equations. . Conservation of mass and definite proportions. Equivalenf weights and reacting weights. Problems dealing with equations. Molecular and atomic weights as relative rather than absolute weights. 3. How the equation represents volume relationships. Representative of gaseous conditions only. Relationship between coefficients and G. M. Q.'s represented. Problems dealing with equations. Unit V.
Ionization and Ionic Reactions
1. Dissociation in solution. Differences between the solutions of ionogens (ion formers) and of nan-ionic substances. Characteristic reactions of the ionogens (acids, bases, salts). Relationship between dissociation and csrrying capacity for electricity; between dissodation and degree of acidity or alkalinity; between dissociation and abnormality of changes in h. p. and f. p.; betkeen dissociation and the degree of concentration of the solution. C 2. Characteristic reactions among ionogens. Why characteristic only when in water solution. Chemical equilibrium in solutions. The dynamic quality of chemical equilibrium. Conditions which will prevent equilibrium and cause reactions t o go t o completion. Double decomposition as a type of chemical change. Why neutralizations go t o completion. Unit VI. The Metallic and Non-Metallic Nature of the Elements
1. Characteristics of the metallic elements. (Consider iron, copper, lead, gold, calcium, platinum, silver, potassium, sodium, cadmium, and magnesium as representative.) Physical properties; luster, sp. gr., malleability, ductility, tenacity, hardness. m. p. and b. p.. formation of alloys, conductivity. Chemical properties; formation of positive ions in solution; formation of basic oxides; the displacement series, with applications. 2. Characteristics of the non-metallic elements. (Consider carbon, sulfur, oxygen, nitrogen, phosphorus, and the halogens as representative.) Physical properties; make numerical comparisons with the metallic group on the basis of the nine physical properties cited. Chemical properties; formation of negative ions in solution; formation of acidic oxides; displacement series with applications and relationship t o atomic weights. 3. Characteristics o j the intermediate groups. (Consider arsenic, antimony, zinc, aluminum, chromium, and manganese as representative.)
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Physical properties; compare with metals and non-metals. Chemical properties; either basic or acidic reactions of oxides, depending on the other reagent. Types of compounds formed by these elements. The gradual gradation from the most metallic t o the most non-metallic characteristics among the various elements. Unit VII.
The Nature of Chemical Action Involvh~gOxidation and Reduction
1. Simple oridations hrought about by atmospheric oxygen. Burning of fuels; rusting of metals; oxidation and combustion; three factors necessary for burning; conditions necessary for putting out fire; kindling temperature and spontaneous combustion. 2 Simple rcduclion processes brought about by carbon. Reduction on the charcoal stick; heating in closed containers in presence of carbon; reduction of metallic ores by the use of coke or coal; practical applications in metallurgy; roasting compared with reduction; iron smelting; hydrogen as a reducing agent. 3. Oxidation end reduction as reactions which primarily involve changes i n valence. Other oxidation and reduction reactions than those involving carbon and oxygen. Reducing and oxidizing agents; what happens to them in reactions. Practice in recognition of oxidation and reduction reactions. 4. The chracleristic reactions of common ozidieing agenls. Sulfuric and nitric acids as oxidizing agents; potassium chlorate, permanganate, and diduomate; aqua regia; bleaching powder; chlorine; hydrogen peroxide; manganese dioxide. 5. Othn effects of oxidation and reduction processes. Bleaching; killing bacteria; removing ink stains; etc.
Of the three remaining units, one will deal with the "Periodic Classification of the Elements," another with "The Influence of Modern Chemical Knowledge in the Development of Industry and Medicine," and the third with some phases of organic chemistry. The less able student may be able to complete only eight units, while the be& ones may need an extra one. The analysis of simple unknowns by blow-pipe and closed tube methods would be suitable for special work for this latter type of student. As a final word, it may be well to call attention to a feature in the unit organization of a course that is too often overlooked. In order to be really teachable, in that it is possible by means of the unit to lead the student to the place that he can predict behavior, the unit must be explanatory and not purely descriptive. "Copper and Its Properties" is not a satisfactory title, since it is necessary only to present a series of facts in order to satisfy the title. There is no necessity for tying these facts together by means of a unifying principle. No dynamic relationship is involved. The cause and effect relationship must be the basis for unification, since prediction of behavior is thereby made possible. "How" questions are the ones around which the course must be organized; "what" questions are valuable only as a means to the end. To give the proper starting point for organizing a unit, the title, "Water," would be entirely inadequate. "How Water Acts as a Solvent," would be a very decided improvement. The former leads to description only; the latter requires explanation.
