letters Potential for a Water Heater
To the Editor A not unimportant error in thermodynamics involving the use of a numerical value for E", a t 25" C, hut used over a temperature range of 60°C, should be brought to the attention of your readers in connection with Slabaugb's paper on corrosion, [J. Chem. Educ., 51, 218 (1974)l. In discussing the galvanic potential developed in a household water heater as the result of a temperature difference of 60" between the top and bottom of an iron tank, the Nernst equation was used. The correct galvanic potential, assuming dynamic equilibrium, can best he calculated from the entropy change when iron is oxidized a t one end of the range and iron(ll) ions are reduced a t the other. Running quickly through the math, we have
American (June, 1959, p. 1601, a t which time the name of the game was spelled "Eleusis," and the game was referred to as "a remarkable new card game invented by Robert Ahbott, a young New York writer." Gardner also pointed out that the rules had been printed and were available from the Association of American Plavine Card Manufacturers. When combined with the scoring svstem described hv Gardner, the game is not only closeiy analogous to the scientific method of inquiry, but provides long hours of stimulating mental exercise for practicing scientists a t any level of sophistication from the high school classroom to the university research laboratory. I hope readers who were interested in Ziegler's account will not hesitate to expand their attempts at Eleusis.
Charles L. Lerman Juniata College Huntingdon, Pennsylvania 36652 Radiation Safety
The value of A S can be calculated for the above process, assuming that C , for iron and iron ions is independent of temperature. Inserting that value into the relation stated V above, one obtains a potential difference of 2.5 x between the top and bottom of the water tank, instead of 0.004 V as cited in the article. Jay A. Young Auburn University Auburn, Alabama 36830
Origin of "Eleusis"
To the Editor: I read with interest G. R. Ziegler's note 151,532 (197411, about his classroom use of the card game he calls "Eloosis," because I have had the pleasure to indulge in this game recreationally with other scientists for several years. My first acquaintance with the game was in Martin Gardner's "Mathematical Games" article in Scientific
To the Editor: A recent article by Richard Hernnann [J. Chem. Educ., 51, 420, (1974)l concerns the preparation of radioactive sources hv s e ~ a r a t i n eand concentratine radium from radium diai alarm cloeks or World War l f ~ r m compasses. y I believe that the described procedure for removing the radium paint with acetone is unsafe. The author mentions several other precautions to be taken in treating the radioactive material during the radium concentration procedure, hut he seems to overlook the hazards from the emanation .--~ .....of radon from the ....radium.
The author measures readings of 50 mr/hr a t 8 cm for his radium source. This indicates that the source contains about 0.4 mCi or 8 X 108 disintegrations per minute (dpm) of radium. During the course of the pro'cedure (hours) about 0.4 mCi or 8 X 108 dpm of radon (or 4 X 109 dpm of alpha activity) will become airborne. If the room for the experiment is 10 m3 (with no ventilation), there will be 80 dpm of Rn/cc. The maximum permissible conpCi/cc centration of Rn-222 for a 40-hr week is 3 X or 6 X 10-= dpm/cc-a factor of a thousand times less than produced in this procedure. (The MPC is ten times less for young people.) If the room is adequately ventilated the radon concentration will be diluted and the student could receive an insignificant dose. On the other hand (1)the student could be working close to the ema-
Volume 52, Number 3. March 7975
nating source and receive a much larger dose, and (2) unless the radium source is properly sealed, about 109 atoms of radon will eet into the atmos~hereof the room everv minute as long as the source is in the rbom. A radioactivity survey of the room longer than a few hours after the experiment to check for contamination will not disclose whether hazardous quantities of radon had been present a t the time of the experiment. Daniel L. Love Nuclear Chemistw Division Naval Surface Weapons Center White Dale Laboratory Silver Spring, Maryland 20910
molecule in a cube or how carefully we lead up to i t from lahoratory experiments or demonstrations, a true understanding of the equation will be heyond the comprehension of most students. PV = nRT will remain a black box. I don't believe the purpose of teaching or of "covering" gases is to enable facile gas law calculations. Pedagogically, gases are studied in the introductory course because they provide evidence for the existence of molecules and demonstrate the kinetic molecular theory. The principle that one mole of any gas occupies 22.4 1 under standard conditions is a confirmation of Avogadro's hypothesis, a tangible comparison of gaseous versus liquid volumes, and very concrete evidence of the distance between gaseous molecules. 22.4 is also an excellent operational definition of a mole of a gas. And, with a little thought, 22.4 can be used to solve any gas law problem. William W. Schweikert
To the Editor: The State of Connecticut, Department of Environmental Protection, sent a responsible health physicist to the school to inspect the area soon after the article was puhlished. One of the items he was concerned about was the radon factor. After 1%hours of examining all aspects involved such as room size, ventilation, sources, etc., he was satisfied that no appreciable hazard of concern was present. Richard A. Herrmann Science Dent, ~ ~ ~ Griswold High School Jewett City, Connecticut 06351
Some People Love 22.4 To the Editor: I take issue with Dr. Rubin Battino's comments regarding "22.4," which appeared in the August, 1974 issue of this journal. As a high school chemistry teacher, I have sound reasons for promoting the molar gas volume and for eradicating PV = n R T 22.4 is not a number pulled out of a hat and engraved on the classroom wall. The students have obtained it by sweating over measurements in the lahoratory, calculating the corrections to STP, and averaging the class data. The number is quite meaningful and concrete. Starting with 22.4 l/mol students can reason out any gas law problem. Is thinking dangerous or inconsistent with educational goals? "Learn-it-hy-the-rules-or-else,"indeed! For most students, P V = nRT is the golden rule for gases. It is the "one-step talisman" par excellence, the magic formula that students have been searching for. Plug in the numbers, turn the crank, and the "right" answer comes out. Of course it always works; it will work even in the first chemistry class of the year. We can have the students plugging into P V = nRT and churning out the "right" result on the very first day. Better yet, why not program the computer so they haveonly to punch in the given values? Without getting into Piaget's theory of cognitive development, let me add that it is presumptuous to assume that half of high school juniors or even of college freshmen really know what an equation is all about. The reasoning and formal thinking involved are heyond their present abilities. Given the ideal gas law, can students qualitatively predict the effect of varying the parameters or graph the equation? I think not. No matter how elegantly we derive the ideal gas equation from the kinetics of a 204
l Journal of Chemical Education
Vorthfield Mount Ikrman Sehnal Marsachusetts 111351
To the Editor: Professor Battino's polemic 151, 526 (1973)l concerning the work and motivation of high school teachers and textbook authors is out of place. He offers no solutions to his prohlems hut to "let George do it." He hlames authors for writine to their students (or colleames) . not his. Like all speciaksts he decries any attempt to teach his specialty in a limited introductory way t o beginners. He complains about rote learning of 22.4 l/mole at S.T.P. and its misuse in problems and then asks for rote learning of how to manipulate logs without understanding. Students' inabilities to learn facts and to think cannot he categorically blamed on their Dast teachers. I t is entirely appropriate for Professor Battino to provide limited material consistent with the limitations of his clientele, hut not to complain because other educators don't provide the materials for him. I look forward to the appearance of his text, and promise not to draw conclusions as to his motiuations for writing from its contents.
G. P. Haight University of Illinois Urhana, Illinois 61801
To the Editor: In the experiment on the "Reduction of CuO with Burner Gas" by Zidick and Weismann [J. CHEM. EDUC., 50, 717 (1973)], the apparent danger of working with an open flame and the possibility of student misadjustment of the flame after it has been reduced to a reasonable size makes the set-up pictured in the experiment somewhat unsafe. Our freshmen have performed this same experiment for the past five years using a modified set-up which is shown in the attached diagram. In this set-up, the open flame is avoided by recycling the excess hurner gas into the burner used to heat the CuO. The heating time for the reduction of the CuO with this set-up based on past experience, is about 5-10 min using a 1.0 g sample. In addition, the cooling process of the test tube and copper metal is speeded up by removing the hurner after the reduction and allowing the hurner gas to continue to circulate through the apparatus. David A. Katz Community College of Philadelphia Philadelphia, Pennsylvania 19107