HOSMER W. STONE University of California, Los Angeles
Tm
treatment of the problems of instruction as research projects often yields a stimulating and exciting experience for both the students and the instructor. Many such problems arise when the large number of students requires the use of graduate students or even fellow staff members in the quiz and laboratory work. An example of a fundamental and frequently unsolved problem is that of persuading the students to think. The students in beginning chemistry may be classified as belonging in one of three categories: (1) those who are content to memorize the material of the course for the purpose of regurgitation during examinations; (2) those who memorize not only the material but also some of the logical reasoning sequences of the course (the latter is illustrated by the use of the memorized solution of a type problem as one might use a mathematical formula); (3) those who, in addition to the essential memory work, look upon chemistry as something to be understood. They are able to use the knowledge obtained for original thought processes. This understanding and ability for logical thought, with new association of ideas, is characteristic of the student in contrast with the mere enrollee. I n a previous publication2 the author presented data and drew conclusions on the topic, "Do Students Think?" The results indicated that approximately 10% of the two classes studied, naturally fell into class 3. Under stress produced by repeated quizzes and the warning of continuing quiz work on the same type of problem, 20% more of these classes were pressed into doine some original thinking of a sort. Thus a total Presented before the Division of Chemical Education at the 132nd Meeting of the American Chemical Society, New York, September, 1957. a STONE,H. E., J. CHEM. EDUC.,13, 316 (1936).
VOLUME 35, NO. 7, JULY, 1958
of 30% in each of the classes, independently studied, demonstrated a capacity for thinking along chemical lines. Two projects are now described in which the students were encouraged t o think. The method used is that of asking questions and seeking the answers by means of experiments. The students are asked t o predict the results of certain proposed experiments. The answer is then obtained by means of an experiment. This is followed by asking for an explanation of what actually did take place during the demonstration. In a laboratory experiment involving the determination of the equivalent weight of a metal, the members of the class were required to collect hydrogen gas over water. I n doing this they were directed to fill a liter flask full of water, close the flask and invert it with the mouth under the surface of the water in a basin. This mas to be accomplished without allowing any bubbles of air to enter the water-aled flask. To eliminate the difficulty of entering bubbles of air the students were instructed to place a filter paper over the mouth of the flask filled to overflowing with water. The flask could then be inverted in the air without supporting the filter paper by the hand and without the loss of any water or the entrance of any air bubbles. Those observing the demonstration for the first time are greatly interested. They find it difficult to accept the observed fact that atmospheric pressure keeps the filter paper and water in place. Each member of the class was asked to make a written prediction as to what he thought would be the course of events if the water-filled flask, sealed with filter paper, were to be supported in the inverted position for an indefinite period. No bubbles of air could he seen to enter the flask past the point of contact between
Flask filled with rater, before
inverted flask, alter standing 20
inverting.
days.
the filter paper and the mouth of the flask. As time passed a space appeared a t the upper surface of the water which continued to grow from day to day. (Not,e: If the mouth of the flask is irregular, bubbles may sometimes be seen to enter the flask. The bubbles may be eliminated if the mouth of the flask is ground to a flat surface before using in the demonstration. With most flasks this is not required.) It was found that a liter flask set up in the inverted position with water and filter paper in place lost 54% of the water in sixty days and all of the water in one hundred days. When the possibilities of this demonstration as a tool for stimulating the student's thinking were recognized, it was greatly expanded. Various shapes and sizes of vessels were used. Variations in the liquids and the diameter of the mouths of the vessels were introduced. The effect of using filter paper of different diameters with the same vessel was tried. Paraffin paper and aluminum foil were used as a replacement for the filter paper. An assortment of these demonstrations mere set up where the class could observe, hut not dist.urb, them from day t o day. I n order to stimulate participation by all the members of the class, written quizzes were given which included such questions as: Will the filter paper remain in place indefinitely? Predict the effect of using filter paper with more overhang. Could one remove the paper from the inverted vessel without all of the water falling out? Surprisingly enough, the answer t o the last question is yes, if a 1- X 7-cm. test tuhe is used. Under the conditions obtaining, the water evaporated from the inverted tube from which the filter paper had been removed a t a rate of more than a centimeter in height per day until by the end of the fourth day all the water had evaporated. Using two other 1- X 7-cm. test tubesfor the demonstrat,ion, one closed with a 4-em. diameter filter paper and the other with a 2.2-cm. filter paper, predictions w r e requested as t o the probable difference in the behavior toward the loss of water. The experimental answer, subsequently obtained, showed that with the 4-cm. diameter paper all the water evaporated in 7',12 hours while with the 2.2-em. paper it took 17 hours for all the m t e r t o evaporate.
The effect of using liquids with higher or lower vapor pressures a t room temperatures than that of water was suggested. Diethyl ether and a petroleum fraction boiling from 30'-3G°C. were used to answer this one. Mercury offered an intriguing liquid as an example of one with a lower vapor pressure because it also had the property of not wetting the glass or the paper. I t turned out that it could only he caused t o remain in the inverted tube with the greatest difficulty when the 1- X 7-em. tube was used, and then duplication of the demonstration was uncertain and very frequently did not work a t all. Aluminum foil was used in place of the paper in the f e n instances vhen the inverted tuhe retained the mercury. The use of solutions in place of the pure liquid suggested questions and experiments involving the measurement of molecular weights and the degree of dissociation. A comparison of the effect on the rate of loss of solvent between one containing the pure solvent and another identical one save that it contained a solution of known concentration might be used t o measure these two properties. A crit,ical answer with logical couclusions was given full credit even though the specific experimental answer differed from the predicted one. Of course, when the prediction was not fulfilled by the experiment, a n explanation of what actually happened x a s in order. I n fact, questions requiring that the student explain what actually did happen are often as stimulating and thought-provoking as any based on a prediction of what is expected t o happen. A colleague was certain that a paraffined tube with a paraffin paper closure would not support the water in the inverted t,ube. A .iu-ager x a s won r h e n the experiment proved that such a demonstration wonld work. An observation of the difference between the solubility of nitrogen and of oxygen in water led t o a great deal of original thinking on the part of the instructional staff as well as of the students. Oxygen is about twice as soluble in water a t room temperature as nitrogen. With its greater density it should diffuse more slowly than nitrogen. The greater solubility of oxygen might be taken as an indication that there is a greater tendency t o solvate than is the case for the nitrogen. This information together with t,he composition of the air (approximately 21y0 oxygen to about 79% nitrogen) was presented t o the class. Then it was proposed that the residual gas might have a different oxygen-nitrogen ratio than the air. Speculation as t o the possibility of separating oxygen from nitrogen by some sort of a recycling treatment of the residual gas led to a rash of "Rube Goldberg" devices. The experimental answer t o this problem was obtained by setting up five footlong tubes in a thermostatted room and accumulating, over a period of weeks, a considerable volume of the residual gas. There was sufficient gas for a number of macro determinations by standard gas analysis procedures. A control analysis of the atmospheric oxygen content was run and no difference found hetween the composition of the residual gas and that of the atmosphere. Why there should be no change in the oxygen-nitrogen ratio proved t o be a challenge t o the instructor as well as the students. Perhaps a check on the oxygen content where certain other selected liquids
JOURNAL OF CHEMICAL EDUCATION
were used in place of water would provide the data needed for a satisfactory answer. Another demonstration3 well adapted to the "question- and answer-by-experiment" method is one in which 1-in. X 3-ft. aluminum rods were placed on a 1-ft. cube of dry ice. This produced a loud and continuing noise which was brought t o almost deafening proportions by increasing the number of rods until the surface of thecake of dry ice was completely covered with the vibrating rods. After some minutes of this uproar the rods were removed. The class was made aware of the of heat, that the dry ice was constautl~sublimingand giving off quantities of dense cold carbon dioxide gas, and that there appeared to be no diminution in the intensitv of the noise during the several minutes in which the demonstration was allowed t o continue. The students were then permitted, and indeed encouraged, t o ask any questions of fact concerning the details of the demonstration (Fig. 2). It was suggested that the next hour quiz would contain questions concerning the demonstration. These might include: How long would the sound have continued if the rods had not been removed from the dry ice? Explain the source of energy which produces the noise. How would an increase in the relative humidity affect the demonstration? Would an increase of several fold in the diameter of the rods alter the character of the demonstration? What would be the effect of heating the overhauging ends of the rods on the loudness and extent of the noise and so on? After the quiz sections of the class had met, some of the teaching assistants came t o inquire as to the correct answers to these questions. Their students had been trying t o find the answers to memorize for use on the
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STONE,H. W., J. CHEM.EDUC., 26, 481 (1949).
VOLUME 35, NO. 7, JULY, 1958
rigure2
~ i and length ~ differences ~ elwlge ~ the "itch t :but~ I , R \ Q l i t t~l r e ~ e con t the volume of the noise. This is true of eo,,"er and aluminum but not of iron or steel.
forthcoming quiz. Of course, there were no specifically correct answers required. Credit would be given for logical original answers, arrived at by applying the kinetic theory to the observed facts. Evidence of original thinking was the answer sought. Both students and teaching assistants seemed to have responded to the thought stimulation of the demonstration, and perhaps some who had been only enrollees belonging to class 1 had an inkling of how the students of class 3 were proceeding t o obtain an education in chemistry. Although mauy more questions and experimental answers could be suggested, enough have been given to show how the technique of thought-provoking questions and experimental answers' can he used to stimulat,e original thinking in a chemistry class. Many students found pleasure in these questions and experimental answers who would ot,herwise have been content with the minimum of thinking involved in the "tried and true" memory system with which they entered the course.
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