ROBERTREEVE; Marlborough School
250 S.Rossmore Avenue LOSAngeles. CA 90004
Saturated and Unsaturated Fats An Organic Chemistry Demonstration Rick Broniec J. I. Case High School, 7345 Washington Ave., Racine, WI 53406 The concept of saturation is important to include in a high school unit on organic chemistry. I t is important for students to understand the differences in reaction between saturated and unsaturated compounds, yet i t is often difficult to find illustrative laboratorv exercises that can he done within the constraints of equipment and time of a high school course. The ease of oxidation is a simple laboratory test that distinguishes saturated from unsaturated compounds. I use the procedure on fat-containing foods, which serves to present the original concept and makes a useful extension. As a bonus, I find that my students are very interested in the related questions ot health and heart disease. The term "polyunsatur;ttl.d fats" appears90 regularlv in telrvision commercials and in magazine and newspaper articles ( 1 4 ) that i t is easily recognized in the context of the laboratory exercise. The results of this experiment can lead to discussion and investigation of such related areas as digestion chemistry, enzymes, hydrogenation, fat processing, the nature and sources of animal and vegetable fats, and the relationship between heart disease and saturated fat consumption. Some of the substances used in the tests present possible hazards. Thus. i t is imperative that students he carefullv instructed in the' safe handling of these materials and carefully supervised while thev are in use. Special attention is reauired inthe heating of flammable hydrbcarbons; a w a t e r bath is recommended. Cyluhrxanr and cyclohexene were chosen as standard test materials hecnuse both liquids are commonlv available in the high school laboratory bkcause the struct&al difference is easily seen and because neither is considered to be particularlv toxic ( 5 , 6 ) .I encourage substitution of other hydrocarbons andlor fats in the testing process: the more, the merrier! I t should be noted that because of the imrniscihility of water-soluble reactants and fats, careful mixing and shaking ~f the stoppered test tube is required to ensure sufficient contact between the reactants. Another possible difficulty is an apparently ambiguous result upon testing with the permanganate. This occurs because there are two possible permancanate reduction ~roducts.One is manganese dioxide. a hrown solid that forms in the majority of cdies. The otheris the areen MnO.,-' rmilnranate) ion. Student frustration can be alleviated if any change from the initial purple color is ac. c e ~ t e das a positive test for unsaturation. I have s&cessfully used this experiment at Case High
320
Journal of Chemical Education
School for the nast seven vears. Not onlv does i t seem to help students understand the cbncept of s a t i a t e d and unsaturated compounds, hut it also invariably sparks a lively discussion on the health aspects of this subject. Recent articles help to make the students aware of the importance of limitinn their intake of saturated animal fats ( 1 4 , 7 ) , and thus these students may become more conscientious consumers as well as better chemistry students. ~~
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Procedure Standardizing the Permanganate Test 'To separate l-mL portions of cyclohcxane and ryclohcxcnr add I mL6M NaOH and2mL0.1 A l KMn04.0bserverautions.Stopy~er the tubeand shnkr. Unstopper and warm ina water bath for 21)s. Note the color after 2 min. Testing Foods for Unsaturation Obtain l-mL portions of butter, margarine, lard, vegetable shortening, peanut butter, corn oil, and vegetable oil. Test each separately by adding reagents as above and thoroughlv mixinewith a stirringrod. &pperihe &be and shake; unstoppe~and warm. Data is recorded in a simple grid format. My lab handout asks several questions requiring consideration of the data. Conies of thestudent renort form includine these auestions can be obtained by wiiting David ~aul'el,~ i School ~ h Chemistry Office, American Chemical Society, 1155 16th Street, N.W., Washington, DC 20036. Ask for experiment 1001. Literature Clted
(41 Gwd Hauaekorpig, 95. (Nov.I.311(1982). (5) Flinn Scientific. "Chemical Catalog Referenee Manual: 1982, p. 20. (61 "Manual on Occupational Safety and Heallh,). State of Wiscansin, May 7, 1982. p.
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New lectwes and laboratmy experiments an0 direct ons 'n teachmg cnemisny through Uw dse of Uw btaralov are provoded m lh 5 featre Experimentsare fully detailed ana are I eld tested oeforethey are pdblished. Gontributions should be sent to the feature editor.
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