HIGH-SCHOOL CHEMISTRY DEMONSTRATIONS* RUFUSD. REED, STATETEACHERS' COLLEGE, UPPER MONTCLAIR, NEW JERSEV
The value of lecture demonstration in all science work has been tested by several investigators. Their work has been published in educational journals and as dissertations and some have escaped the notice of abstracters of chemical literature. This paper reports the findings of these investigators and presents a list of experiments suitable for lecture demonstration in a high-school course in chemistry. Why Demonstrate Experiments? In a series of experiments by W. W. Carpenter' it was found that: The majority of students in high-school laboratory chemistry classes, taught by the demonstration method succeed as well as when they perform the experiment individually, if success is measured by tests which measure specific information and ability to think in terms of chemistry. The students of medium and lower intelligence seem to profit on a whole a little more from a good demonstration than when they themselves perform the experiments individually. We may assume further that those students who did write up the demonstration experiments with the same care as taken in writing up an experiment performed by themselves, would on the whole profit practically as much by that experiment as they would have profited if they had performed the experiment themselves on condition that the number of experiments performed individually was not too small a number and that success be interpreted as ability t o succeed in terms of the tasks as measured by tests. It is consistent to believe, however, that high schools can profitably increase the amount of experimental work presented by demonstrations, thus giving the student the benefit of a larger number of excellently performed manipulations and a wider and more thorough use of the experimental method. The increase in number of demonstrated experiments should be larger than the decrease in number of experiments performed by individuals. Demonstration will succeed in developing thinking in terms of chemistry; i t cannot be expected t o develop manual skills.
Substantially the same conclusions were reached by Knox2 and H. A. Cuningham3who found . ..that in explanations of experiments the demonstration-trained pupils did better than laboratory-trained pupils.
What WiU the Lecture Demonstration Not Accomplish? Horton found4from extensive experimentation on ability of pupils to do laboratory work that: * Presented before the Symposium on "Lecture Experimentation," Division of Chemical Education, a t the 77th Meeting of the American Chemical Smiety, Columbus, Ohio, April 29 to May 3, 1929. "Administration of High-School Chemistry." p. 44. 1925. Bureau of Puhlications, T. C., Columbia University. The School Rmiew, 35, 385 (1927). ' 'University of Illinois. Bulldin, 18, 1C5-7 (1920). ' outcomes of Individual Laboratory Work in Chemistry," p. 20, 1928. Bweau of Publications, T. C., Columbis University.
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NO~EMBER, 1929
The (high-school) pupils trained by the individual laboratory method are actually able to do an experiment in the laboratory better than the pupils trained by demonstration method, both groups having been previously taught this experiment by their respective methods.. . Practice in the laboratory results in greater facility in handling apparatus and in doing tasks which call for such handling. Doing other laboratory work was not able to transfer this training a t once.
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From the experiments of these men one can conclude: 1. For imparting information in high-school chemistry which can be tested by written tests: pupils succeed better by observing the demonstration of the experiment rather than doing the experiment in the laboratory. 2. The demonstration method as a means of teaching a pupil how to assemble apparatus and to do tasks is inferior to the laboratory method of teaching chemistry. Another thing which apparently is accomplished is to inspire in students a desire to do more work in chemistry. How potent is this factor is an unmeasured quantity. What Should Be Given in Demonstration? Horton rec~mmended:~ The presenting by demonstration the important phenomena and experimentation of which an undentanding is required and on which written tests will be based. The laboratory will be used t o give practice in handling apparatus and in attempting t o solve problems by supervised but undirected experimentation.
However, one questions the leaving out of too much laboratory work because (1) students will be unfamiliar with the habit of carefully following directions. It is probably axiomatic that chemistry students must learn to follow directions (even if i t is cook-book chemistry) if they do much with chemistry. (2) Many pupils like laboratory work and enjoy chemistry because they can do things for themselves. Technic of Demonstration The apparatus should be simple and of common materials. Complicated and unfamiliar apparatus would merely confuse the student and distract his attention from the main features of the experiment. Excess apparatus should be removed from the table. Experiments should be chosen which yield results that are visible from all parts of the room. The reduction of metallic oxides by aluminum is an example of an experiment which gives visible and obvious results. The testing of the solubility of oxygen in water by shaking a tube of oxygen with a little water and noticing the suction on the stopper is a poor lecture 6
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experiment. The solubility of ammonia in water is a much better experiment. Any experiment .should be tried out previous to class time with some of the materials to be used in class demonstration so as to avoid disconcerting, unexpected results. The object of the experiment should be clearly and simply stated. After performance of the experiment the pupils should be questioned on the object of the experiment and their observations. Any points not clear to the students should be discussed. The essential points of the experiment should be driven home. Equations for the reactions should be worked out. Applications of the experiment should be discussed. Coopridge found by test experiments6that It is better to give oral instructions for demonstration experiments than a typewritten sheet of instructions.
Should Students Write Up the Experiments? The information retained by classes, one of which wrote up the experiment and the other did not, was measured by giving an unannounced test 24 hours after the experiment was performed. Then the class which had written up the first experiment was given a second experiment, a write-up for which was not required and the class which did not write up the first experiment was given the second experiment and was required to write i t up. Both classes were tested again after 24 hours. The results obtained were as follows: Class A Class B Class A Class B
Median score on test 1 over experiment which was written up Median score on test 1 aver experiment which was not written up Median score an test 2 over experiment which was not written up Median score on test 2 over experiment which was written up
8.53 7.20 8.42 12.88
... Sum of median scores on both tests over experiments which were written up Sum of median scores an both tests over experiments which were not written up
...
Difference in median scores
21.41
15.62 5.79
These results indicated that the median score on tests over experiments which were written up was 37 per cent higher than the median score on experiments which were not written up. Experiments Recommended for Demonstration Accepting Horton's criteria: 1. Demonstrate in high-school chemistry those experiments which explain important chemical phenomena and laws. 2. Perform individually experiments which give practice in handling apparatus. The Chemistry Teachers of Northeastern Ohio recom6 Sck. Sci. Math., 23, 526 (1922).
mend the following list of experiments to be given as separate demons t r a t i o n s or as supplemental to individual laboratory experiments. This list is s o m e w h a t similar to the list of lecture demonstration topics given i n the Report of Committee on Order of Procedure of Laboratory and Recitation in High-School Chemistry.' It gives specific experiments rather than topics as given by the committee. It does not purport to be all inclusive and doubtless no one teacher would perform all the demonstrations.
A.
COMPLETE DEMONSTRATIONS
1. To determine the weight of one liter of oxygen. 2. To determine the amount of a metal which will set free one gram of hydrogen. 3. Boyle's Law. 4. Charles' Law. 5. Conductivity of acids, bases, and salts. 6. Supersaturated solution and crystal growth. 7. Destructive distillation of coal or wood. 8. Preparation and properties of amme nia including ammonia fountain. 9. Preparation and properties of hydrochloric acid. 10. Preparation and properties of chlorine. 11. Preparation and properties of carbon monoxide. 12. Etching with hydrofluoric acid. 13. Phosphorus and its acids, burning of phosphorus and observation of the products. 14. Marsh's test for arsenic. 15. Goldschmidt themite process or reduction of oxides by aluminum. 16. Operation of carbide lamp.
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