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HIGH-SCHOOL CHEMISTRY
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Some Observations on the Teaching of Chemistry CHARLES H. STONE Vermont Junior College, Montpelier, Vermont
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HREE transcontinental trips have afforded the wnter . opportunities for visiting a considerable number of preparatory schools. Certain conclusions have been drawn from observations made in the chemistry classes in these schools. It would be idle to say that these conclusions are general, for it is impossible for any one person to visit each of the 20,000 high schools in this country; but the various faults cited below have been observed in many schools, and it is believed that they may be noted in many more schools than the writer was able to visit. The following are noted, not all, of course, in any one school. 1. Dependense upon the text. Teachers are often observed who sit a t the desk with the book open before them, asking questions from it and apparently verifying the pupils' answers by reference to the book. What confidence can a class have in an instructor so obviously dependent upon the textbook? An instructor in any subject who cannot go into his classroom and teach the day's lesson without so much as looking in the book doesn't know his subject as he should, and can hardly expect to win the confidence of his pupils. Of course, he must turn to the text when outlining tomorrow's lesson, when calling attention to some paragraph which may require special study, when directing attention to the diagram on page 35 that he wishes the class to reproduce, and the like; but in general, the less the book is used in the classroom the better. The teacher should be the master of the situation, not the servant of the printed page. 2. Failure to use demonstrations. Too frequently, in answer to the question: "What are you doing with the class experiment a t the teacher's desk?" the answers have been: "Oh, we don't do anything with that here" ; or, "We are not equipped for such work" (as though a demonstration experiment required elaborate apparatus and unusual chemicals); or, "I have so many classes I just can't find time to set up apparatus and prepare for such work" (legitimate excuse probably); and, most surprising of all, "I don't do anything with demonstrations because I don't believe in them. It is better for pupils to do their own experiments than for the teacher to do them for the class." This teacher evidently did not distinguish between a demonstration experiment by the teacher and a laboratory experiment by the pupils, two phases of the work which may be, and often should be, markedly diierent. It is inconceivable that any teacher can fail to see the great value of demonstrations as a means of stimulating interest, clarifying certain matters, and in general increasing the efficiency of the instruction.
3. Lack of resourcefulness. Here is a case: The laboratory directions for an experiment call for lead nitrate but there is none in the stock room, although there is lead oxide and lead carbonate. The teacher announces that the experiment will be deferred until a supply of the missing chemical can be obtained. In 10 minutes that teacher could provide the class with enough lead nitrate by the simple expedient of treating the available lead compounds with nitric acid. It may often happen in any laboratory that some chemical may be lacking but there is a good chance that the missing substance can be prepared on the spot. Many of the chemicals in ordinary use in a school laboratory can be prepared as a project by some of the abler pupils. Barium chloride from the carbonate, copper sulfate from the oxide, mercurous nitrate from liquid mercury, and lead dioxide and lead nitrate by treating red lead with nitric acid are examples. A summer course in "Inorganic Preparations" would be an invaluable aid to teachers of general chemistry in high schools, and so would a course in "Methods of Teaching Chemistry" but few of our college summer schools offer them. 4. Failure to follow u p the subject. Every teacher, I suppose, lays much stress on Priestley's experiment with mercuric oxide, but by inference leaves the pupil to suppose that any other oxide would serve the same use. Without telling the pupils anything, call several of them to the desk and let each one heat the oxide assigned him, testing carefully for oxygen. No simple oxide will give this tgt. With this evidence, it is not difficult for the class to amve a t the conclusion that simple oxides do not yield oxygen when heated. What does your textbook say about this? 5. Failure to enunciete a general firincifile. The text tells George that lime, CaO, is obtained by heating limestone, an impure calcium carbonate, CaCOs. True, of course, and you can show this in five minutes a t the desk. But what happens when other carbonates are heated? CaU to the desk several students and, without telling them anything, let each heat, respectively, the carbonates of lead, copper, cadmium, zinc, cobalt. In each case decomposition follows with evolution of carbon dioxide and formation of a residue of oxide. Extend this investigation further if you wish and show that the carbonates of the alkali metals are not decomposed, while the carbonates of metal: low in the displacement series are decomposed to the metal. On the basis of this investigation, the class may formulate a general statement, noting the exceptional cases. Isn't it better for Johnny to have a clear understanding
of the general statement covering a large number of cases than i t is for him to try to remember one isolated instance? 6. Failure to use practical tangibles in place of textbook intangibles. Not very long ago the writer visited a high school and found the teacher of chemistry disengaged. In reply to the question, "What are you teaching now!" the answer was, "I am teaching equations." "And how are you teaching this subject?" "Why, from the textbook; what other way is there!" "Would you mind coming to your laboratory and learning how to teach equations without any book a t all, provided pupils know their table of common valences?" So we went to the laboratory and samples of solid potassium iodide, lead nitrate, and potassium nitrate were placed on the desk. A little potassium iodide was put into a test tube and handed to the teacher who now took the part of a pupil. "Describe this substance." "It is a white solid." "Add a little water." "The solid dissolves." Similar treatment was given to a small sample of lead nitrate, hut this time the "pupil" found that heat and shaking would hasten solution. "What color are your two solutions!" "They are white." (Usual answer.) "Do you mean they are whitelike paper?" "Oh, no, I don't mean like that; they are colorless." "Pour one solution into the other." The "pupil" did so and a bright yellow substance formed. "What. is this yellow substance?" The "pupil" did not know. "Please write the equation on the board." The equation was correctly written. "What are the two products of this reaction?" "They are lead iodide and potassium nitrate." The bottle of potassium nitrate was placed forward. "What color is "It is white!" "Could the yellow this substance!" product in your test tube he potassium nitrate?" "Why, no! It couldn't. Oh, I see! The yellow product mnst be lead iodide!" And so we went on with half a dozen other similar equations. At the end, the "pupil" said: "I've learned more how to teach equations than all I learned in. the college where I studied." This method was so amazingly simple and yet this teacher had never thought of using it. Equations are generally regarded as an uninteresting topic, but taught in this way they become fascinating, for the pupil can never tell just what is going to happen since a variety of colors may result in different experiments, and there is always the element of suspense. 7 . Too much telling. Many instructors seem to think that a11 that is expected of the pupil is that he shall remember-remember what the text says and what the teacher tells him. Memory, of course, is very important and we cannot go very far without it. But there is another factor of prime importance, wie., to develop in the pupil the ability to observe closely, t o think carefully, to reason from noted data to some definite conclusion, and to keep an open mind and modify such conclusions as other data are discovered. The instructor tells his class that most carbonates are insoluble in water; that is an intangible. Instead, he may call to the desk half a dozen youngsters and, with-
out telling them anything, have each of them experiment with the solubility of the carbonate assigned to him. The uniform results observed, some questions asked, some thinking required, and a definite statement should easily be formulated. This method takes more time, but it is superior to the telling method in the long run for the experimental approach deals with tangibles. I n one minute an instructor can tell his class what is the effect of the formation of an insoluble product in a reaction between a liquid and a solid. But better, he can call to the desk Anne or Abel and direct the pupil to add dilute sulfuric, nitric, hydrochloric acids to some marble chips contained in three test tubes. The reaction starts off merrily in all three cases, but soon one of the reactions slows down and finally stops. Don't tell the pupil anything. Some such questions as these may be asked: "In these three reactions just where must the chemical action take place?" (Chemical change must occur a t the surface of contact.) "Is there water in the dilute acids used?" (Yes.) "If the substance formed a t the point of contact is soluble in water, what will happen?" (It will dissolve away as fast as formed.) "If the product formed on the contact surface is not soluble in water, what will happen?" (It will remain where formed and gradually build up a fence between the acid outside and the marble inside; thus a separation of the acid from the marble occurs.) "Is calcium sulfate soluble in water?" (Not very soluble.) "Do you see then why this particular reaction slows down and stops?" The pupil may now be asked to give a complete statement of the case. I n some such way the instructor may lead his pupils along the road of observation and reasoning using the method of tangibles. Which will Abel remember longer, your intangible statement or the result of his own experimentation under direction? 8. The inane question. One is often surprised a t the type of questions asked by teachers. "Oxygen is prepared by beating potassium chlorate, isn't it, Jennie!" And of course Jennie says it is. "Hydrogen is prepared by the reaction between sulfuric acid and-." To this George replies solemnly, "Zinc." What intellectual activity is developed in the pupil by such questions? The question which suggests its own answer is another useless type. "Manganese dioxide and hydrochloric acid react to produce chlorine, don't they, John?" And John declares they do! And if the teacher had said: "When sulfuric acid and zinc react, the acid drives the hydrogen right out of the zinc, doesn't it, Walter?" Walter would probably say that it did! It is so easy for pupils to follow the line of least resistance, instead of the mental development that follows the question which suggests no answer hut which puts the pupil on his own to stand or fall. Then there is the question devised by the meticulous teacher who wants to cover all possibilities. "Mildred, what would yon say is the general reaction between acids and metals, excluding those metals high in the displacement series and theFefore too active, and those low in the series which are inactive, and excluding those
acids which are only feebly ionized such as acetic acid and those which have oxidizing properties such as nitric When the teacher has finished that question acid!" the pupil's head is in a whirl.
The whole subject of the methods of asking questions has been set forth by Romiett Stevens in a pamphlet published by Columbia University as a master's thesis. The contents are most interesting and valuable.
