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tested demonstrotions Corn Chip Aroma A Classroom Demonstration on the Preparation of a Schiff Base Antony T. Sartori and William F. wood' Humboldt State University Arcata. CA 95521 Checked by:
Leonard C. Grotz University of Wisconsin, Waukesha Waukesha, WI 53188 Chemicals with pleasant odors have been the subject of very few classroom demonstrations. In fact, most odors associated with chemicals made in chemistry laboratories and classes usually are considered obnoxious. 3-Methylimino-2-butanone (1)has a n intense, pleasant aroma of corn chips and can be prepared easily during a lecture from small quantities of 2,3-butanedione (21,
0
C-C-C-CH3
N/cH3
0
11 11
CH,NH,.HCI
base
II II
CH~--C-C-CH~
methyl amine hydrochloride and a base. The reaction takes place within a few seconds and emits a n odor that is immediately recognizable by most individuals as a corn chip aroma; however, some individuals indicate it has a popcorn-like scent. This demonstration can be incorporated into a lecture on the chemistry of Schiff bases and imines. This lecture also can point out that chemicals with similar shapes and functional groups generally have similar odors.
GEORGE L. GILBER; Denison University Granville,OH 43023
it in a solution that contains 0.1 g of this compound per liter of water (3).As can be seen from their structures (below), these two compounds have similar shape and so likely bind to the same olfactory receptor. Reactions of aldehydes or ketones with primary m i n e s are well known. The product is a substituted imine and is frequently referred to as a Schiff base. For the purpose of this demonstration, methylamine hydrochloride is reacted with a sodium hydroxide solution to make methylamine since the latter compound is a gas a t room temperature. All volatile components used in the preparation of the compound are found in food consumed by humans. 2,3Butanedione is found in butter and is used as a food additive to i m ~ a r at butterv taste to food oroducts. Methvl amine is f&d in crab and other seafod. The fairly reGI tive com~ound.3-methvlimino-2-butanone.readilv undergoes &mehzation or hydrolysis back td the st&ing materials. Thus, it must be prepared fresh for each demonstration. Experimental Procedure Before lecture mix 0.43 g (5 mmole) of 2,3-hutanedione and 0.33 g (5 mmole) of methylamine hydrochloride in a test tube with a cork stopper. When the demonstrator is ready to produce the corn chip odor, slowly add a mixture of 1.0 mL of 5 M NaOH and 1.0 mL 95% of ethanol to the test tube and restopper it (heat evolved, color change). After gentle shaking for one minute, the stopper is removed and the odor of corn chips can be detected. Do not smell t h e test tube because the odor quality changes in high concentration! In large lecture halls it may be necessary to walk up and down the aisles to disperse the odor adequately. Stopper the test tube when the demonstration is finished to contain the odor. Literature Cited
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4.Schieberle.P.: Gmseh,W.Z.Labensm.-Untsrs. Forsch. 1985,180, 4141478
Red, White, Blue, and Yellow Chemistry Phyllis D. Dewar Chowan College Murfreesboro,NC 27855
The compound 3-methylimino-2-butanonewas prepared bv Thomas H. Parlimcnt of the General Foods Corooration a i d has been patented as a flavoring for foodstuffsil). This compound hab not been found in nature but mimics 2-acetvl-l-ovrolline (3)u mmoound that is associated with the pleas& odor of cooked cereal products ( 2 4 ) .The human nose is very sensitive to 2-acetyl-l-pyrolline and can detect 'Correspomlence may be addressed to this author.
572
Journal of Chemical Education
As patriotism peaked during the recent Gulf War and the United States flag was seen with increasing frequency, I was reminded of the acid-base colors of Congo red. This indicator undergoes a blue to red change in color at approximately pH 3.0-5.0. It is common knowledge that reactions can be done on paper, so why not make a United States flag? A convenient size for a flag is that of a large sheet of chromatography paper, 46 x 57 cm.The stripes, about 3.5 em tall, are cut from another sheet, color developed, and then taped to the white flag base. To develop the red stripes, dip the strip of paper into a 0.1 M NaOH solution, spread to dry on paper towels and spray with Congo red indicator solution (0.1%in water). Darker colors can be obtained by allowing the paper to dry and spraying repeatedly with the indicator solution. A square is cut for the
background of the stars and sprayed with 0.1 M HCl. To develop the blue color, spray the square with Congo red; the stars can be attached to a plastic food wrap and placed on the blue background. As with any demonstration, the success and usefulness of its presentation are hindered only by the imagination of the demonstrator. I generally try to keep a lively dialogue going while I am attaching the strioes to the flae. ~ u r i the n ~same time frame, I also was reminded of the 1970 Rov Lichenstein work "Peace throueh Chemistrv" which features the colors red, white, blaFk, and yellow. When a local third grade student was asked to draw a picture about the War, he drew what he thought was an appropriate picture and then wrote "Peace is a big, fluffy cloud of very bright yellow with red, white, and blue streamers." I have used this third-grader's idea as a demonstration. The big, fluffy yellow cloud is simulated by placing on a lighted magnetic stirrer a 4-L beaker containing dilute sodium iodide solution. A few crystals of lead(I1) nitrate are added t o produce a bright yellow cloud of lead(I1) iodide. Streamers developed using Congo red are hung between the beaker and the stirrer. Chen's ( I )''American Flag" does not produce flag-like colors. However, he does offera good flagpolesuggestion,i. e., treat paper with tannic acid (2%)and spray with imn(II1) chloride (1%)to produce gray-black iron(II1)tannate. Literature Cited
S.
E"*rtai"ing ~d Edumfional ChDmirol I * m o M t m t i o ~ ;Chemical Ekments: Csmsdlllo, CA, 1974: p
1. Chen, P.
20.
Simple Soda Bottle Solubility and Equilibria Cheryl A. Snyder
Penn Manor High School E. Cottage Ave. Miiiersvilie. PA 17551 Dudley C. Snyder
Penn State University Wilke-Barre Campus Lehman, PA 18627
pour out approximately one-third of the contents. Add 2-3 drops of bromocresol green indicator, and reseal the bottle. The solution should he clear-yellow. Allow the bottle to warm to room temperature. Green. Then shake the bottle vigorously, and carefully open the cap to vent the pressure of the C02. Repeat the process several times until little pressure remains. At this point, the solution should be clear-green. Blue. Place the open bottle in a bath of almost boiling water and wait. Within a few minutes the solution should turn completely blue. Discussion
Although the students may recognize that gaseous C02 can be dissolved in water (eq I), they may not know the chemical reaction that generates a small equilibrium concentration of carbonic acid (eq 2) in solution. Yellow. This equilibrium concentration is shown by the initial yellow color, which is the color of the bromocresol green indicator' at a pH below 3.8 (eq 3). When the bottle warms, the solubility of the C02 decreases, but the resulting pressure in the sealed container prevents any significant change. Green. Only when the bottle is opened and the C02 is allowed to escape do the three coupled equilibria shift. The rise in the pH is seen as the indicator moves into the transition range of 3.8 to 5.4. Blue. Since some COz remains in solution even at ambient pressure, heating the solution to a higher temperature is required to drive out the residual gas. The pH then rises beyond 5.4, where the indicator is blue. Comparlson with Other Demonstrations
This process clearly demonstrates the effect of both temperature and pressure on gas solubility, as well as Le Chatlier's Principle in all three equations. It has some similarity to Shakhashiri's2 pressure-variation demonstration, but it has several advantages. It is simpler to perform, and it requires no special equipment. Also, a larger volume of solution is used, and this provides better visihility.
Checked by:
Ronald E. DiStefano
Northampton Area Community College Bethlehem, PA 18017 Recently while searching for a simple visual demonstration of gadiquid solubility, we found success using a simple bottle of seltzer water and an acid-base indicator. The chemistry of the demonstration is summarized in the following equations.
Demonstration
Use a 296-mL clear-glass bottle of plain seltzer water, which is available in most supermarkets. Only seltzer water with no colorings, flavorings, or other additives should be used. Colors could mask the indicator change, and other materials such as phosphates might buffer the system. Yellow. Remove the label, and wol the bottle in an ice bath. Then open the bottle, and--as quickly as possible--
The Use of Potassium Alum in Demonstrating Amphoterism Kris F. Tesh Vanderbiit University Nashville. TN 37235
The property of amphoterism is surprisingly difficult to demonstrate. Almost all introductory chemistry texts state that A1203 is an amphoteric compound that undergoes the following reactions: NzO8(s) + 6HCl (aq) + 2AlC4 (aq)+ 3H20 Commercially available aluminum oxide does not always read as these equations suggest. Only the y-form of A1203 displays reactivity toward acids and bases. The more common a-form is made by heat treatment of the other forms of the oxides and hydroxides of aluminum(l), and is stable 'CRC Handbook of Chemistry and Physics, 51st ed.: The Chemical Rubber Co., 1971;pD-106. 'Shakhashiri. B. 2. Chemical Demonsiraiions-A Handbook for Teachers of Chemistry;University of Wisconsin Press, 1985;Vol. 2, p117. Volume 69 Number 7 July 1992
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