further combined these coincidental observations they generated a hybrid structure 4, which was also a sweet tasting suhstance. The close resemblance of structures is quite evident in the AORTA view, which indicates an A H - 5 x 2 hypothesis (Fig. 2). The carhoxylic acid function (red) is extremely important to sweet taste since analoeues (8)incorp o r a t i n g h ktheaboveregionswith asulfoniracid (red) are bitter 5.6. A structure with the absence of an, acid is denatoniumbenzoate 7, the most hitter compound known (9). Llterature Clted 1. Dsstoii. F. R: Price, S. Science 1986,154, 904. Hiji. Y.; Kobeyashi; Sam. M. Comp. Biochem. Phmiol. lWl,3+B,367. Hiji. Y. Nature 1975,256,427,Chem. Eng. N e w 1981,(Ds27). and reference therein. 2. Kato, Y.: h i , A,; liraka, Y. Tetrahedron L987,43(22),5229. ConnoUy,M. QCPEBuII. 1981.1,75. 3. Shalienborger,R.S.:Ai\ri\i\,T. ENotura (London) 1961,216,480:J.Agrie.FoodChom. ,.""", am . ,7.,"", 4. Kier, L. B. J. P h r m . Sci. 1972,61,1394.See a h Ciajoio, M. R.;Ldj, F.;Tsncredi, T.; Temussi. P. A.:Tuzi, A. J. Med. Chom. 1983.26,1060. 5. Tauehiya, T., et si. Ajinomoto, Co.,Jpn. Kokai Tokkya Kaho JP 62,252,754. 6. Petersen, S.; Mulier, E. Chom. Bor. 1948,81,31. 7. Tsuchiys, T., et at. Cham. Abrr. 106:214377j to Ajinomoto, Co., Jpn. Koksi To& Koho JP 61,260,052; Chom. A b t r 107:196772y to Ajinomoto Co., JP 62.132,&17: Chem. Abstr. lOE:75851k to Ajinomoto, Co., JP 62,132,863. S Research Triangle Institute, Chemistry and Life Sciences Group, Life Seienaa and
Tarimiw Di"8i.n. Final R e ~ roft Contract No. N01-DE-02428 submitted to the Office of Collaborative Research for The Nationd Institute of Dental Research; mmpound RTI-2075-014andRTI-2075-011. % The Memk Index, An Encyclopedia of Chomicok, Dm#*,ond Biolw'caB, lOth ed.: Rahviay, NJ, 1983:p 417.
A Microscale Study of Gaseous Diffusion Dlanne N. Epp East High Schwl 1000 So. 70th Lincoln, NE 68510 Edward J. Lyons East High School 1000 S. 70th Lincoln, NE 68510 Davld W. Brooks Center for Science. Mathematics,and Computer Education University of Nebraska Lincoln. NE 68588 Demonstrations or experiments involving gaseous diffusion are limited in number1, perhaps due to the difficulty of handling and observing gases. The following microscale experiment compares qualitatively the rates of diffusion in air of chlorine molecules and ammonia molecules. I t may he projected conveniently on a n overhead projector or carried out as a hands-on laboratory exercise. When working with a nonuniform mixture of gases, the gases diffuse into each other until a uniform composition is achieved. The classical work performed by Thomas Graham2 and since discussed by other^^,^ showed that, a t constant pressure and temperature, the rate of diffusion is inversely ~rooortionalto the sauare root of the densitv of the eas. 'Moiar mass is often sibstituted for density. 1f 'the gasesare diffusing into air, a more general statement can he developed that relates the rate of diffusion to the concentration o f t h e gases. Procedure Prepare the cover of a 96-well flat-bottom plastic tissue culture plate by drilling small holes near two opposite comers of the cover (see figure). The experiment is carried out an a clear acetate sheet.
'
Shakhashiri,B. 2.ChemicalDemonshations, Volume 2 University of Wisconsin: Madison. 1985: pp 55-74. 2(a)Graham,T. Phil. Mag. 1833,2:175,269; Graham, T. Phil. Mag. 1833. 2:175, 351; (reprinted in Graham. T. Chemical and Physical Researches; Edinburgh University, 1876; pp 44-70.) Mason, E. A,; Kronstadt, B. J. Chem. Educ. 1967, 44. 740. *Kirk, A. D. J. Chem. Educ. 1967,44,745.
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Journal of Chemical Education
I
grid on acetatesheet DlfhBlon apparatus.
Draw a l-cm grid the size of the cover onto the sheet. Use the reverse side of the acetate sheet to prevent interaction of the chemicals with the grid lines. Grid lines may conveniently be printed onto an acetate sheet using a suitable transparency maker. Leave 2 x 2 corner squares of the grid (to he located under the holes in the cover plate) empty. To each of the other squares in the grid, add 1drop of 0.1 M KIIphenolphthdein solution. (To 100 mL of 0.1 M KI add 2 mL 1%phenolphthalein solution.) Cover the grid with the prepared cover plate. Through one comer hole add 3 drops of bleach to the center of one corner square. Working quickly, simultaneously add 2 drops of 3 M HCI to the bleach through the cover hole above the bleach and 3 drops of concentrated ammonia to the center of the emotv . . sauares . in the opposite corner of the grid. Cover both holes with small pieces of tape. Observe the color changes with rime for several rnmutes. Wash the acetate sheet and plastic cover at a sink with large arnnunts of running water. Reactions and Conclusion Bleach contains chloride and hypochlorite ions. A strong acid will cause chlorine gas to be released from the solution:
+
C1 CIO-
+ 2Hf +Clz + Hz0
The progress of the chlorine gas as it diffuses is observed by the formation of colored iodine molecules as the iodide ions at the surface of the KI drops are oxidized: Cl* + 21-
= I2 + 2CI-
The progress of the gaseous ammonia molecules is followed bv the effect on phenolphthalein when the extremelv soluble ammonia molecules &ssolve and form a basic solution in the aqueous K I solution. By following the color changes in the KI/phenolphthalein solution, students observe several important features of diffusion. First, although the gases are diffusing into air, which impedes their progress, the net movement of the gases is rather rapid. Second, i t is readily noted that the lighter ammonia molecules (17 glmol) diffuse more rapidly than do the heavier chlorine molecules (71 glmol).
Rotation of Polarized Llght by Stereoisomers of Limonene Sally Solomon hexel Unlverslty Phlladelphla,PA 19104 Equlpmenl and Chemicals overhead projector two 10-mLbeakers four squares of Polaroid HN film cut from a 15- X 15-cm square' (R)-(+)-Limonene;9790~ (S)-(-)-limonene; 97V
