Robert Korplus Deportment of Physics University of California Berkeley
Chemical Phenomena in Elementary School
T h e title has been chosen to indicate that I consider elementary school science to be an interdisciplinary program in which chemical phenomena as well as others contribute to broaden the pupil's experience and understanding. Most of the students in elementary school will not become scientists. Though they cannot devote much time and effort to education in science, all of them seriously need to have some grasp of scientific attitudes, procedures, and concepts. Unfortunately, the adult population a t present seems to haveonly avery poor understanding. Since it is clear that science will continue to play an increasingly significant role in every individual's life, it is important that educational practices be adapted so as to prepare the students more effectively to meet the challenges that will face them. The chemical phenomena I have in mind are those in which specimens are transformed so as to change their macroscopic appearance. On the scientific level, one reconciles these phenomena with an intuitive awareness of conservation by interpreting them as the consequence of the rearrangement of atoms, molecules, or ions, which themselves are conserved. For the uninitiated, however, there is a strong magical quality in such transformations as the production of silver chloride from waterlike silver nitrate and sodium chloride solutions, or even the solidification of liquid phenyl salicylate. I n this article I shall try to indicate how the Science Curriculum Improvement Study2 is approaching the incorporation of chemical phenomena into an elementary school science program. First, I shall describe some characteristics of elementary school science as they are determined bv the nature of the student ~onulation. Second, I shall point out certain difficulties 'that are presented by chemical phenomena. Third, I shall sketch several conceptual tools that may help in the teaching program. Finally, I shall give some examples of chemical processes that have been included in the curriculum. Since elementary schools are attended by all children, one should view the study of science as a part of general education. One may use the term "scientific literacy" to denote the functional understanding of scientific concepts and the inquiring mental attitude that the school tries to develop in the students. The teaching objective Part of the Symposium on Elementary School Science presented to the Division of Chemical Education at the 149th Nat,ional Meeting of the American Chemical Society in Detroit, Mieh., April 6, 1965. ' The Science Curriculum Improvement Study is supported by the National Science Foundation. KARPLUS, R., "The Science CurriculumImprovement Study," JRST. 2. 293 (1964): and SCIS NmZetlws., De~artment of . ~ h ~ s i e university s, if'California, Berkeley.
is to give them sufficient knowledge and experience so that they will have some understanding of their natural environment and an appreciation for original scientific work carried out by others. Two aspects of the necessary teaching program may he differentiated from one another to good advantage. The first of these involves giving the student experience, offering him opportunities to observe a wide variety of natural phenomena. The second involves introducing the student to an analytical approach that modern scientists find useful in thinking about the phenomena they study. Let me give some examples of what may he done to provide the students with experience. The observation of phase changes on heating and cooling, of animals carrying out their habitual behavior, of magnetized or charged objects attracting or repelling without contact, and of the growth of plants, are all useful in helping to form a picture of the broad range of natural phenomena that do occur. Also necessary are more "elementary" experiences with the change in appearance of a liquid sample as it is transferred to differently shaped containers, with the "feel" of specimen of very low or very high density, with the appearance of colored objects in a monocbromatically illuminated environment, and with the details of surface structure that become visible when a mineral specimen is examined with a magnifying glass. I n all these cases, it is essential that the experiences be direct ones for the student. To see photographs and to read descriptions are completely inadequate substitutes for observing phenomena oneself. For the children to draw useful long-term impressions from their experiences, they must learn to observe more analytically. Young children ordinarily tend to take a subjective and global approach. To distinguish the material objects participating in a phenomenon from other aspects of the phenomenon is not a trivial differentiation for the pupils to make; for instance, to separate the "spinning" from the "top" when they observe a spinning top, or the air in a tire from the pressure exerted by the air-after all, how often do they hear the statement, "Put more pressure into the tire?" Once objects are recognized, changes in the appearance or motion of the objects can also be recognized and can be interpreted as evidence of interaction among the objects. I n this way, cause and effect relationships are introduced. Finally, interacting objects can be grouped into a system of objects to be studied, while everything else is considered as background or environment. The interactions within the system and the system-euvironment interactions can then be taken up separately. Chemical reactions will he included as resulting from a special kind of interaction. Volume
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To some of you, these distinctions may seem rather pedantic and superfluous. Do not all people learn them sooner or later? Would it not be more efficient just to postpone science instruction until juniorhigh school, and to concentrate then on more strictly scientific topics? Unfortunately, a survey of the adult population indicates that the ideas I have described do not become well established. Instead, each individual develops a pattern for thinking about natural phenomena that may be called a personal natural philosophy. With most persons this natural philosophy is colored by the prevalent cultural attitudes and superstitions, such as those that have to do with the relation between drugs, diet, and health. This coloring in turn reinforces and perpetuates the cultural modes of thought. Only in a small minority of students does the personal natural philosophy overlap substantially with modern scientific attitudes; these students are then identified as the science-oriented ones. For the others, their personal natural philosophy b e comes a fixed part of their thinking patterns and forms an effective block to their learning science later. The antipathy of many liberal arts students toward science courses is well known. Indeed, it should be expected. After all, in their science courses the nonscience-oriented students have to learn a different way of understanding a natural universe with which they have already come to terms. Not only does new theoretical understanding appear to them superfluous; their very observations of natural phenomena are biased by their preconceptions and expectations. L. L ~ w e r y a, ~graduate student in science education a t Berkeley, recently studied the stereotypes that develop. Working with fifth graders, he found that in some communities 40% of the boys associate science with monsters and destruction and that 30y0 of the girls associate science with health and medicine. Almost none of the children associated science with experimentation or with specific natural phenomena. Another difficultywith the natural philosophy is that the individual is usually not aware of whether his ideas and beliefs are based on evidence or on faith, and which ideas constitute defi~tions. In addition to the lack of experience with natural phenomena, children lack manipulative skill. I n combination, these factors result in certain problems. The first, as I have already mentioned, makes chemical changes seem magical, mysterious, and beyond the realm of systematic explanation. The second raises the questions of health hazards and safety. Open flames, breakable equipment, and toxic substances can be introduced into elementary classmoms only in carefully controlled situations that limit experimental investigation by the children. Yet it is necessary for the children to make extensive observations of chemical changes before they can recognize chemical properties and other systematic features of the phenomena. Another way of stating the difficulty is to point out that the children's environment is highly inert in a chemical sense. Chemical changes just do not occur subject to their observations. (This also is a consequence of the health hazards associated with reactive substances.) No wonder, then, that the L O ~ R L., Y , "An Experiment,al Investigation into the Attitudes of Fifth Grade Students Toward Science," unpublished doctoral dissertation, University of California, Berkeley, 1965. 268
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evidences of chemical reactions appear to be magic! Let me add that these factors, which are problems for the educator, make chemistry exciting for children. The scientist has developed certain conceptual tools to cope with the problems of understanding the existence and regularities of chemical processes. The most important of these is his view that substances are composed of structural units such as molecules, ions, atoms, or electrons and nuclei, as the discussion requires. It is inevitable that this model be introduced in order to put all of the children's observations on a rational basis. The big question is, when? How much background must the children accumulate before an explanation based on structural unity makes sense to them, and how many impressions can the children retain without confusion before these are organized by a structural explanation? No systematic work has yet been undertaken to clarify this point. We do know, however, that even though words like "atom" and "molecule" are part of the children's cultural environment, most of them do not relate these words to any real phenomena. The words do not have an operational meaning. The other conceptual tools are two laws of thermodynamics: the conservation of total energy in an isolated system and the irreversibility of the approach to equilibrium of an isolated system. Both of these can be treated macroscopically and are therefore independent of the teaching about structure. The latter, as I shall show with an example in this article, appears to be easier to introduce with children because it concerns the observable properties of a concrete process, while the former concerns the properties of a hypothetical construct--energy. Illustrative Activities
I shall describe some activities that have been used by the Science Curriculum Improvement Study. I n the first grade, for example, children dissolved a given sample of sodium chloride, let the water evaporate, then redissolved and re-evaporated many times one after another. They observed that the salt always remained in about the same amount and had a similar appearance. After a while, they gained the impression that the salt was present in the colorless liquid even though they could no longer see the grains that had been visible originally. This awareness is part of the concept of conservation of matter: a substance that is put into a container is in the container until it is removed or permitted to escape. Second grade children prepared a solution of copper chloride and water and then introduced aluminum foil. The solution of copper chloride was blue and therefore provided some evidence of the continued presence of the copper chloride. When the aluminum foil was dropped in, the formation of bubbles, the reddish copper deposit, the increase in temperature, and the ultimate discoloration of the solution all furnished evidence of interaction between the aluminum and the copper chloride. The children recognized the evidence and gained further experience with a chemical change, but some of them concluded that the aluminum was burning up. Even though this seems strange to an adult, it was not so far fetched. Burning is the one dramatic chemical change children know; furthermore, the temperature rise, the
reddish-blackcolor, and thedisintegration of the foil (like burning paper) all supported their conclusion. Clearly, children need to become familiar with a wider variety of chemical changes. The solution process was taken up again in the third grade. Children placed a soluble salt in a tea bag in a jar of water and then observed the schlieren (not introduced by name) produced when the solution streamed out of the tea bag and flowed to the bottom of the jar. The visible evidence, i.e., the disappearance of the salt in the tea bag and the stream emerging from it, fascinated them greatly. I n seeking to explain the phenomenon, one child pointed out that the tea bag was "unfinished" paper and that the salt disintegrated into little bits that went through the holes in the paper. Later in the year, the third graders observed the melting and solidification of phenyl salicylate in their own teaspoons placed an alcohol flame or in cool air. Here again the most ready analogy, that the "salt" had turned to "water" which then "dried up" and left a crust of "salt," was used by quite a few children to describe their observations. I should add that the "water" response came from many children who had had the previous experience with solutious, and it also has come from quite a few liberal arts college students in a physics course I have taught. The analogy with melting ice is perhaps the reason for calling the liquid ',water." The analogy of the solidification of phenyl salicylate with water freezing to form ice did not come up. Apparently, freezing implies a temperature much lower than that which occurs in the experiment. Other possible experiences with paraffin, butter, and cooking fat are not connected with the melting of phenyl salicylate by the children either. With third graders and with older children the concept of an equilibrium state and the approach to eqnilibrium have been introduced. Of course, the experiences with solutions, with the changes that are brought about by temperature differences, and with mechanical
systems gave the children a fairly broad background for the idea of an equilibrium state. Studying the approach to equilibrium was another matter. Since phenomenaoccur irreversibly, it isdifficult to become aware of irreversibility as a macroscopic law of nature. Unfortunately, it is not possible to set up a laboratory demonstration of a system which departs from equilibrium spontaneously. One may, however, project motion pictures of an irreversible process so as to create a time-reversed illusion. Accordingly, children were permitted to see a film in both directions and were then asked to identify, with supporting evidence, the normal or "forward" sense of time. Interestingly enough, some children became aware of their own inability to make a determination because they recognized an absence of criteria in some scenes. A child hopping up and down rapidly, or a child slowly stirring a homogeneously colored liquid presented this difficultythese scenes could have been projected in either direction. When an inhomogeneously colored liquid was stirred, however, the children were unanimous in determining the "forward" sense of time. I hope that these examples suggest how chemical phenomena can contribute to the elementary school science program, but much more needs to be done than I have described. Clearly, older children must become acquainted with the stoichiometric relations that are characteristic of many chemical changes. And, as I have pointed out before, an operational understanding of the structure of matter and of energy and energy transfer must be communicated. Now, how can chemists contribute to educational progress? There are many opportunities. They may participate directly in planning the curriculum. They may further the education of college students who are planning to become elementary school teachers, but who are fearful of science courses. And finally, they may alert the schools in their communities to the new ways in which science education is being viewed.
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