edited bv GEORGEL. GILBERT ~~
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Denison University Granville. Ohio 43023
A Useful Balloon Demonstration: Pressure
Difference Behavior SUBMITTED SY
SUBM~TWBY
Ariel A. Fenster
Bruce G. SmlIh
John Abbon College St. Anne de Bellewe,
Davld N. Harpp
Appleton High Schwl-West 610 North Badger Avenue Appleton, WI 54911
McGill Unlverslty Montreal, (lue., H3A ZK6 Canada
CHECKDBY
Joseph A. Schwarcz
Kenneth H. Lothrop
Vanier College Montreal, Ow.. H3X ZN9 Canada
Marshfleld High School Marshfield, MA 02050
CHECKED BV
I have taught chemistry in a high school of about 1800 students for six years. Over this time, I have found the subject of atomic structure and theory to be one of the most difficult about which to incite enthusiasm in my students. Most related demonstrations on the topic, although informative, are hardly exciting to the beginning student. A very good analogy to Rutherford's experiment can be demonstrated in the classroom in an interesting and humorous way using simple equipment. I have had difficulty getting my students to visualize the possible results of firing a small particle a t a solid crystal arrangement of atoms. I finally came upon the following method. I obtained a model of some solid crystal lattice with space between the locations of the atoms. I am sure several typesof classroom models would he usable. However, I found the diamond model from Lab-Aids, Inc., Bohemia, NY (Catalog No. 501) to be particularly effective. I t contains about five or six layers of atoms depending upon how i t is oriented. This represents Rutherford's gold foil. I then obtained a particular "gun". I found an old buret to make an effective "pea shooter". Peas, which represent a heam of high-speed particles, are fired a t the model one a t a time and the results observed. Some are reflected back, some are deflected part way through the foil, and some particles pass directly through. I feel it would be difficult to quantify this demonstration, for you are not getting the proper statistical distribution, and "detecting" the particles may prove intractable. However i t is a very effective qualitative demonstration of an important concept in studying atomic structure.
Quebec,Canada
Luther K. Brlce Virginla Polytechnic instilute Blacksburg, VA 24061
The "crushed can"' experiment in which creation of a pressure differential by the condensation of steam inside the closed container is a classic demonstration used to illustrate dramatically the behavior of gases. Aupropriate solvent .. . cans, how&er, are not readily a&ilnble to most teachers. We wish to report a simple and effective demonstration of the same principle usinga 250-mL Erlenmeyer flask (or in fact any bottle) and a balloon. The flask is filled with water to a depth of about 1/4 in. and is heated until the water just begins to boil. The flask is then removed from the heat source and a balloon previously inflated to a diameter of about 5 in. is placed over the mouth of the flask with a slight downward pressure. Almost immediately, as the vapors in the flask condense and create a partial vaccnum, the balloon begins to be sucked into the flask. Within a short time. the ruhl)rr issrretrhed to such an extent rhat the balloon hursts, clearly illu.;tratina the increasing pressure differential between the air in the balloon and the gases in the flask. An interesting variant on the above demonstration involves inflating the balloon to a diameter of about 3 in. and placing i t on the neck of the flask. The whole balloon will be drawn into the flask.
' Gardner. R.
1978; p 51.
"Magic through Science"; Doubleday: New York,
Volume 63 Number 7 July 1986
629
