Gas laws and gas behavior


Add to this collection Davenport's syringe exper- iments of Boyle's Law that appeared in "Tested Demonstra- tions," J. CHEM. EDUC., 56, p. 322 (May 19...
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mnething new From the pwt Gas Laws and Gas Behavior Gas Laws and Syringes . . Revisited: Boyle's Law In the December, 1980 issue of THIS JOURNAL, p. 885, the work of Derek A. Davenport involving the use of the hypodermic syringe t o study gaseous behaiior was reviewed: His work and similar demonstrations and experiments developed by others are wonderful sources for fun with gases in t h e classroom. Add to this collection Davenport's syringe experiments of Boyle's Law that appeared in "Tested Demonstrations," J. CHEM. EDUC., 56, p. 322 (May 1979). The experiments are easy to do, and typical data (all obtained in 5 minutes) are given. Gauge Pressure and Absolute Pressure On the same page as the Boyle's Law experiment mentioned above, Davenport describes some interesting (and fun) gas behavior using a standard tire pressure gauge and a side-arm test tube. Various pressure readings are made which show, "The sum of the gauge pressure and the residual pressure (in the same units) is sensibly constant!' "When the test tube has been completely evacuated, the gauge reading will be found to have increased by an amount equal to the atmospheric pressure." Who's Law?

"Boyle'slHooke's/Towneley and Power'shfariotte's Law," Robert M. Hawthorne, Jr., J. CHEM EDUC., 11, p. 741 (November 1979). "Chemistrv. .. like all the sciences. is filled with constants...orincioles. . and mathematical laws, many of which havesumeone's nameattached to them." Thestudent ofchrmi~try,knowing no brttrr. ~ s a p toast rume that the prrron named ir the prrwn who actually produced the number or formula that's on the page before him, an assumption often far from the truth. Probably no great harm is done in this way, as the substance of the law is more important than its provenance. Nonetheless, there are some interesting anecdotes connected with the formulation of laws. or the determination of constants. that can he

.A case in point is the gas pressure-volume relationship that we know as Boyle's Law, which has a very tangled origin indeed. It is from articles such as this one that the "s~ice"of the stow of cbemistrvcomes. The sienificanceof the oriori& of ouhlicationand of keeping a lab book is Gressed by the author, read the entire article to get the rest of the story. "The Fable: Laws are Mature Theories," Jack K. Homer and Peter A. Ruhha, The Science Teacher, 46,31 (February 1979). "At the heart of this fable is a fatal assumption about the relationship between laws and related theories: namely, that theories mature into laws by constant testing and confirmation." The authors present three familiar examples that show the fallacy of this common, naive misconception. Boyle's and Charles' laws are used as one of the examplesshowing ". _thatthe relationship between theories and laws is an exolanatorv one-not. as the fable insists. a maturational one." One rentlmg d r h article ~ and many <,Iyou will change yuur teaching, P I ~ P V I H I I ~fur ym1r hrgmning chemistry clssiti.

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"On Avogadro's Number: as Shakespeare's Prospero might write," S. R. Scholes, J. CHEM. EDUC., 42, 126 (March 1965).

Edited by: JOSEPHS. SCHMUCKLER Chairman of Science Education Temple Univerrify 345 Riner Hall Philadelphia.PA 19122 Some of us have had students in our classes whose fortes were not in chemistry. These "bards" were the students who added other dimensions to the class. I recall the delightful surprise I had on reading one student's lab reports written in the style of Coleridge's "Kubla Khan," or Lord Macauly, or Horatius. Can you imagine yourself introducing Avogadro's number in the style of a Shakespearean thesbian? No? Try it. Both you and your classes might enjoy it. "New Device for Determining Molecular Weight of a Gas," Howard Nechamkin. The Science Teacher, 35. 47-48 (April 1968). With today's disposable butane lighters, this experiment is even easier to do than it was using the method suggested by Nechamkin. "Reaction Kinetics" Brian Moar, The Science Teacher, 44, 48 (May 1977). This is a "macro-demonstration" of kinetic molecular theory involving students as molecules in a confined volume (area). "Kinetics Teaching Model," William W. Sadler, The Science Teacher, 38.41 (November 1971). In previous columns we have cited articles on physical models to demonstrate the effects of molecular activity. Sadler describes a simple inexpensivedevice that he has constructed from common items found in most high schools and which can be used with an overhead projector. It demonstrates random motion and transfer of energy as spheres "the size of basket balls" collide on the projection screen. It shows gaseous diffusion through a membrane, and effects of temperature changes and concentration changes. "Analysis of the Upper Atmosphere," William R. Jensen, J. CHEM.EINC.,54.74 (February 19771. 1 have reproduced this short article that can be used as an anecdote in your clar3er. Yuu will haw t~,gotorhejournal for theactual illus. tration. "The illustration shows the balloon ascent made on August 20, 1804, by the French chemist, Gay-Lussac,and the French physicist, Biot, to test, among other things, an earlier Russian claim that the earth's maenetic field decreased with altitude. Their resuits indicated that it was wnstanr. They also tested thr atmosphrrc'~chemical ~.mnpmitimas a fun
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"Illustrating Principles of Kinetic Theory of Gases," Robert C. Plumb, J. CHEM. EDUC., 47, 175 (March 1970), 48, 119-120 (February 1971). and 50,559 (August, 1973). Sea-Lab Experiment frontiers." "The ocean floor is one of our unexolared eeoeraohical .. .. . To extend rxploration of the ocean, scientists and engineers arc drveloping hardware and prucedurri I<,permit pwpk t o live for days or weeks in chambers on the ocean floor. In these chambers oxygen and helium are used as an atmosphere. A strange physiological effect is noted when a person lives in an atmosphere in which nitrogen has been replaced by helium. If the temperature in the chamber is a normal, comfortable 70°F such as is used in buildings on the earth's surface,the aquanauts feel decidedly chilly. Why? ~

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Space Vehicle Reentry a n d Thermal Effects of High Winds "If a person is exposed to a cold wind, he loses body heat more rapidly than he does under circumstances where heat lass is controlled by diffusion-it may evenlead to a tragedy such as on Mt. Washington in New Hampshire when two persons "froze to death" on July 20, 1959, even though the temperature did not go below 3S°F, but the wind was as high as 65 mph. "Why, then, does a space vehicle, in passing a t high speed through the atmosphere, tend to get hotter than the gas? Why doesn't i t get caoled to the temperature of the atmosphere? At what wind velocity would a person standing on a high mountain tend to heat up instead of cooling off, and why in terms of molecular behavior would this occur?" Gas-Bubble Disease of Fish

"A brieht-eved child brines some eoldfish and a fishbowl homelation downstream-e.g., salmon or trout-suffers great losses. If you own a goldfish bowl or home aquarium or are a fisherman or conser-

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Journal

of Chemical Education

vationist, then keeping fish alive and healthy is of concern to you. You will see in this eaemplum how a simple chemical process is a common cause of fish kills; knowing the chemistry leads directly t o solutions to the problem. I n each of t h e above examples of chemical principles you s h w l d read t h e articles in their entlrcts in order tnanswer t h e questions posed b y t h e authors.

A Lab Experiment "Does Pressure of a Gas D e p e n d o n t h e N u m b e r of Molecules?" J a m e s V. DeRose, Chemistry, 38, 26-28 ( J u n e

1965). "The problem of counting molecules in a gas sample would seem to be insurmountable. However, i t is not necessary actually to count molecules t o conduct an investigation which provides data relative to this question." DeRose gives a detailed introduction and procedure to this "Lab Bench" experiment. He presents expected data and a series of good questions that will challenge the students to think.