A SECONDARY-SCHOOL COURSE IN INORGANIC PREPARATIONS ELBERT C. WEAVER Phillips Academy, Andover, Massachusetts
several years we have capitalized on an exceptional interest in chemistry aroused in secondaryschool students. A number of students are in school who have satisfactorily completed their elementary chemistry course, either on this campus or elsewhere. Some of these have program time available for a minor course in the senior year (grade 12), and wish to continue in chemistry. Approximately eight students each year, for several years now, have pursued such a course. The course in inorganic preparations offered to these students is in no sense an attempt to anticipate their work in college. Rather, the course aim is to keep chemistry bright and interesting for later use in college courses. Scattered reports from students lvho have gone on to college show that in a modest measure a t least, the course has been successful in fulfilling its . DUrDOSe. The course comprises one class period per week plus two consecutive hours in the laboratory. Most of the students are willing and even anxious to work more hours than are scheduled. To these, the laboratory is made available. Class time is given to explanation of apparatus and its operation, techniques of operations to be performed, and the chemistry of the reactions involved in the preparations. Time is left for a systematic review of all sorts of numerical problems of elementary chemistry. The material on which these problems is based is selected from various sorts of work in elementary ehemistry. Henre the problems furnish an excellent reviev of the text as well as of stoichiometry. We have used with success the following - texts: FOR
ample, for two years different students have worked on the problem of trying to find the molecular weight of Hevea latex when it is fractionally creamed by ammonium alginate solution. The method followed is similar to that described by K. Van Holde and R. A. A l b e ~ t y . ~ Several dozens of different preparations have been accomplished by students in recent years. They include the ~ n -r e.~ a r a t i oof: 1. Chemically pure sodium chloride from common salt. 2. A double = ~ tsuch as c~(NH,)~(so,)~.~H~o. 3. A complex salt such as CU(NH~),SO~H~O. 4. Sodium perchlorate by neutralization. 5. A"hydrOus chloride. 6. Boric acid and boric oxide from borax. 7. Chromium and other metals by a Goldschmidt reaction. 8. Mercurous nitrate, mercuric nitrate, stannic chloride, ammonium chlorostrtnnate [(NH4)?SnCls],and titanic sulfate solution. 9. Nitrogen dioxide, sulfur dioxide, and chlorine in sealed tubes.
A
Students keep a log-type notebook. The object, sketch of apparatus, weight of yield, percentage of yield, and comments ahout the purity of the product are included in the notebook. Also logged are comments about the procedure, difficulties encountered, and the method used to surmount the difficulties. Apparatus is sometimes improvised. A clay partition-tile insulated nith aluminum foil and heated by a Bunsen burner served as a drying oven until me adapted a used domestic electric baking oven for this purpose. We also use a hand centrifuge, desiccators, suction. funnels, and all of the equipment common to elementary chemistry. A gas-fired furnace mas constructed from DAVIS, ''Synthetic InBUNCHARD, A.A., J. W. PEELAN, AND A. firebricks that once lined the firebox of a steanl boiler, organic Chemistry," John Wiley & Sons, Ine., New York, 1936. constant-tempera'ure bath is stirred by a blo)vpipe ~, WAITON, H. F., zlInorganic preparation^,^^ p r e n t i e e - ~ a ~lnc., mounted in a chuck attached to a small motor. A stuNew York, 1948. dent-made mercury thermoregulator is attached to the with occasional use of necessary relays and to an elertric light bulb that heats HENDERSON, W. E.,AND W. C. FERNELIUS, "Inorganic Prepara- the bath. A "T" connection and a shut-off valve tions,"MeGraw-Hill Book Co., Inc., New York, 1935. placed in the steam line that supplies heat to a radiator The experiments must he selected with care to include in the laboratory makes steam available for steam onlythose within the range of the apparatus available. baths. The jet of steam from this source has roved to course given in grade 16,' we do not be a valuable aid to loosen "frozen" glass stoppers. unlike a send students to source literature other than to THIS Ice is supplied by nature, and from the cube trays of a domestic refrigerator when the natural supply fails. JOURNAL. The compounds made by the students are sealed in Further, students may substitute for this course a pro~ectthat continues throughout the year. For ex- mall jars which are properly labeled, including the student's name. These products make a colorful dis1 GAYER,K. H., AND M. J. ELKIND, "A course in inorganic c 'J. CHEM.EDUC., 26, 151 (1949). preparations," J. CHEM.EDUC30,90 (1953).
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play in the corridor. We have sometimes added a picture of the student at work in the laboratory. Students like to make a tangible product. They have reason to be proud when t,hey have learned to prepare a hydrated salt that while dry lacks the evidence of efflorescence, that is well crystallized, and that gives negative results when tested for impurities. On the other hand, students do not generate much enthusiasm for the problem work of chemistry-with one notable exception. They seem to admire greatly the method for solving mixture problems that is called Pearsons' square. Since Pearsons' square (certainly not original with the writer) is not mentioned in the 25-Year Index of TXIS JOURNAL, two examples of this timesaving method are given here. (1) Problem: Concentrated acetic acid is 17.4 N as purchased. What volume of acid is needed to make one liter of 3 N solution? Solution: Place the given concentration and the acid concentration of water (0) on the left side of a square pattern. Place the wanted concentration in the center of the square. Subtract arithmetically along the diagonals of the square, thus:
The acid to water ratio is 3 to 14.4 or 1to 4.8.
That
is, of 5.8 parts of liquid, one part is acid. 1000 m1./5.8 gives 173 ml. of acetic acid.3 (2) Problem: If 150 ml. of 95 per cent sulfuric acid is mixed with 50 ml. of 43 per cent acid, what is the per cent of acid in the mixture? Solution: 95
\
'
x -43(150)
The ratio of (x - 43) to (95 - x) is the same as that of 150 ml. to 50 ml. Hence x equals 82 per cent. In at least one secondary school, chemical research is carried out that results in papers acceptable to the Journal of the American Chemical Society. While such a situation appears to be an unusual case, a course in inorganic preparations is well within the range of many another seconda~y school. The interest of several secondary and junior-college teachers in this minor course suggests that a similar course offered elsewhere may find ready acceptance. Student interest in the course as conducted here is high. Indeed, it serves as a stimulus to some of the students in elementary chemistry, one of whom is now doing a few of the advanced experiments as an extra-curricular proiect. a This answer agrees substantially with -that given in the "Handbook of Chemistry and Physics," 32nd ed. Chemical Rubber Company, 1951, p. 1415.
