CHEMISTRY

Tmm is something new under the sun in this issue of TEE JOURNAL: the beginning of a monthly page of tested lecture demonstrations in general chemistry. Each issue for the next two years will cover a different topic, 24 in all, so as to encompass the whole area of general chemistry.

Value to the Teacher. Perhaps, as a teacher of general chemistry, you have performed only a few scattered experiments each year because you have not had suf- ficient time to assemble the materials. If so, this proj- ect should help you. For i t will enable you easily to prepare material for an entire year's demonstations in general chemistry. You will note that the demonstra- tions, the first of which series appears in this issue, are marked so that they may be cut out and filed in a loose- leaf notebook as a complete set of lecture experiments.

Topics. The titles for the next two years follow. A. INTRODUCTION

1. Chemical changes 2. Oxygen 3. Hydrogen 4. Water, acids, bases, salts

B. PHYSICAL CHEMISTRY 5. States of matter, solutions 6. Ionization 7. Energy 8. Equilibrium, oxidation and reduction 9. Atomic chemistry, nuclear reactions, planetary

changes

HUBERT N. ALYEA Frick Chemical Laboratory, Princeton, New Jersey

C. CHEMISTRY OF THE ELEMENTS 10. Group O-the air 11. Metallurgy 12. Group I-alkali metals, copper group 13. Group II-alkaline earth metals, zinc group 14. Group III-aluminum, rare earths 15. Group III-IV-boron, silicon 16. Group IV-inorganic carbon 17. Group V-nitrogen 18. Group V-phosphorus family 19. Group VI-sulfur family 20. Group VII-the halogens 21. Group VIII 22. Other metals-Sn, Pb, Cr, Mn, etc.

D. ORGANIC CHEMISTRY 23. Chain compounds, ring compounds

E. COLLOID CHEMISTRY 24. Colloids

Basic Experiments Only. The first 24 sheets of this series will contain basic experiments only. More spec- tacular and dramatic experiments may be known, but their use might not be as good pedagogy. For example, the orthodox experiment on elements, mixtures, and compounds involves a series of tests with iron, sulfur, and iron sulfide; using CS2 to dissolve the S, a magnet to separate the Fe, and HCI and either lead-acetate paper or odor to confirm the sulfide. Now iron, sulfur, and rotten-egg smell are familar to the beginning student,

JANUARY, 1955

and it is therefore good pedagogy to use them in an early lecture. A far more bizarre experiment usinganti- mony, iodine, and antimony iodide involves brilliant color changes. But these rhemicals are unfamiliar to the beginner, and henre are less valuable pedagogically. Therefore iron-sulfur not antimony-iodine appear in this first series.

Later Series: Tested Demonstralions. However, it is planned, after the first 24 sheets have appeared, to continue the series with more dramatic ways of carrying out these and other experiments. To this end chemistry teachers are urged to submit their favorite experiments to Professor Frederic B. Dutton, Department of Chemistry, Michigan State College, East Lansing, Michigan, who will act as editor for this series, receive pour suggestions, and submit them to a panel of teachers for testing in the laboratory. Those demonstrations having special merit will he published later on, with proper acknowledgement to the authors. The demon- strations appearing in this first set of 24 topics have al- ready been tested by the anthor well over half a hundred times.

Terse Instructions. The teacher will find the instruc- t~ons very brief. The equipment is listed; then in hold- faced type is stated what the lecturer does, or what occurs. The instructions are sufficient, however, for certainly a teacher knows what to do if he reads:

1-15 Zn rod, PbAc2-aq., 600-ml. beaker. Form lead tree.

This will be the fifteenth esperiment under Topic 1. The aq. is used throughout the series to desig- nate an aqueous solution of 3-Jf concentration. The esperiment is to immerse a zinc rod in a 3-M aqueous solution of lead acetate. A beautiful dendritic form of metallic lead forms on the rod. In some experiments footnotes amplify the instructions.

Demonstration Kits. Also in the footnotes are indi- cated labels for the teacher to type, fasten to suitable containers, and lay away in kits, so that the set of ex- periments can he repeated several times in one year, and from year to year. Details for making these kits are given in the instructions for Topic 1.

Student Workbook. The author has used these sheets in another way. When he lectures on oxygen, for ex- ample, he distributes a copy of the oxygen demonstra- tion sheet (Topic 2) to each student. At one point in the le~ture he may announce that he is performing ex- periment 2-9. After performing it, he tells the student to write down on the sheet the equation for what oc- curred and the principle being illustrated, pausing long enough in his lecture for the student to do this. This forces the student to think rather than to bask idly in the pleasure of the excitement of the experiment. The sheets, collected a t the end of the lecture, show the lec- turer whether his demonstration was properly under- stood by the class.

DEMONSTRATION HINTS

Teachers are in the greatest selling game in the world-the selling of intellectual curiosity to their students. Some miscellaneous selling tricks are there- fore not amiss at this point.

Lecture Box. A brightly-illuminated lecture box is a prerequisite. An improvement over the box described in THIS JOURNAL (25, 249 (1948)) is a single box 12 in. wide X 10 in. high X 8 in. deep, with a backboard 12 X 7 in. and a gooseneck pipe holding a 150-watt spot- light 18 in. above the platform. Two similar boxes without lights are also useful for occasional experiments, one painted white for colored precipitates and one black for white precipitates.

Special Apparatus. Avoid elaborate pieces of ap- paratus; do not get out a cannon to shoot a fly. Special apparatus which is ready for instant use is preferable to something which has to he lahoriously assembled; for instance, build an electrolysis-of-mrtter apparatus with a self-contained battery. Keep the equipment simple. Elegant as a magnetic stirrer is, for example, the sight of the lecturer stirring the solution with a glass rod is more instructive. Often special precautions, such as unnecessary drying of gases by passing through calcium chloride, are extraneous operations ~rhich obscure the main reaction and only confuse the student.

Manivulative Techniaues. Do not obstmct the view of your apparatus; keep your hands out of the way as much as possible. Arrange the equipment and chemicals in the same sequence as you intend to use them, instead of conducting a frantic search during the lecture. If an experiment fails, do not labor to make it xork, desperately repeating it over and over again until the class feels as desperate as you. Instead, relate why you think the experiment failed and promise to carry it out successfully the next day. See that you do. Experi- ments which fail reflect badly upon the lecturer's abil- ity, or upon his judgment in keeping them in his reper- toire.

Surprise, humour, and truth are the servants of a good lecturer. Surprise is indispensable; employ it where yon can. Let us take the case of mixing 90 ml. ethanol with 10 ml. saturated calcium acetate; a gel forms. The worst way to perform this is to announce that the gel will form, and then mix and stir the solutions until your prediction is fulfilled. Instead, slowly pour alcohol from beaker 1 into the calcium acetate solution in beaker 2; then pretend to pour the mixture hack into beaker 1. Since a gel has formed. nothing pours out, much to the astonishment of the class. Then explain what has occurred. Humor is a lifeline in any lecbure, especially when anything goes wrong. And truth, nothing but the whole truth, will answer. Never fake experiments. If the experiment is so poor that it needs to be faked, abandon i t ; instead turn in thi.9 issue to the page of tested ezpen'rzents which always work!