Using Real World Examples in a Laboratory Program Adrienne W. Kozlowski Central Connecticut State University. New Britain. CT 06050 A course in the Chemistry of Everyday Life which includes a 2 hriwk laboratory component has been developed a t Central Connecticut State University to fulfill one of the general education requirements. While the course covers the traditional chemical principles, illustrative material is drawn heavily from everyday life and care is taken to point out how many chemicals students encounter in their daily life. It is the goal of the course to correlate sources, uses, properties, and structures of these everyday suhstances. Experiments are selected for the laboratory which utilize "real world" examples. Many chemicals come directly from the grocery store with their labels left intact. While several laboratory manuals have examples dealing with chemicals from everyday life (1-4) none had enough to comprise a complete lahoratnry program for this type of course. Therefore, experiments had to be adapted or originated and then orovided to the students as handouts. An outline of the laboratory syllabus is given in the tahle. Synopses of three exercises from the Chemistry in Everyday Life course are presented here. Each of these exercises involve principles and "real world examples suitahle to the very early portion of a general chemistry course. The first two are performed in the laboratory. The third exercise is an out-of-class assignment. Preparation of Soluble Plant Food Students prepare a sample of soluhle plant food in order to learn the use of a halance and to pactice using the metric system. Preparation of the plant fwd is commonly performed on the first dav of the lahoratorv in addition to check-in and introductory hscussions and taces about one hour. Students are encouraged to keeo the olant food and to test its effectiveness as a fertilizer. An outline of the chemistry of plant fertilizers may be found in several introductory texts (5-7). Students are instructed to tare a plastic sandwich hag, measure 2 Thsp of NaH2P02 into the bag and reweigh, then add %cup of KNO:, to the bag and reweigh, mix thoroughly, and label the hag with the contents and directions for aoolication.l Other recipes for soluhle plant food are given in 'The Formula Book" ( 8 ) . Students learn from the variation in the masses of the salts obtained hv the class that determining the mass of a solid with a balance is more accurate than measuring its volume in a cup or spoon. They also learn to estimate masses using the plastic hag (1-2 g), the amount of NaH2P04 (about 25 g) and the bagged plant food (about 100 g) as references. The first question in the write-up of the plant f ( d experiment requests the students to estimate the masses of some common objects such as a postage stamp, key, pair of scissors, peanut, foam coffee cup, and a roll of sticky tape as being approximately 1, 10. or 100 g. They are also asked to perform some calculations to determine the number of erams of the elements notassium. ni" lrogen, and phosphorus in their sample of plant food and the percentages of each in the sample, given that NaH2P04 is 23% phosphorus and KNO:] is 39% potassium and 14% nitrogen. Thev are also suoolied with a set-uo to comoute the ohospho;us as P205( $ 0 ~X 2.3) and as K ~ O (% K X 1.2) Dissolve 1 Tbsp of the mixture in 1 gal. of water. Feed plants evely 2 wk. Keep extra solution in a labeled plastic or glass jar.
Laboratory Syllabus Preparation of Soluble Plant Food Recovery of Sliver from Film Behavior of Metals
Meet the Elements-Nonmetals Recycling an Aluminum Can Solutions to Solutions Natural Indicators and the pH of Household Products Analysis of Antacids Preparation of Soap and Detergent Preparation of Aspirin TLC of Pain Relievers Testing Swimming Pwls
as is customary in analyses of commercial plant foods. T h e student-prepared samples typically run about 10-15-40, which is rather concentrated in potassium. Solutions to Solutions A second exercise entitled "Solutions to Solutions" was devised to aid in understanding the concepts of moles and molarity. While homework problems on these topics are commonly used as drill, the ideas often remain nebulous and abstract to students. "Solutions to Solutions" was set up as a hands-on lah exercise where real solutions were prepared and examined tn illustrate moles of solute and molaritvof solutions in a more concrete manner. In this experiment, students calculate the molar masses of sodium chloride, sucrose, ammonia, ethylene glycol, acetic acid, and sodium hypochlorite and complete a tahle indicating the number of grams in a mole. Then they weigh out one-mole quantities of solute, dissolve in various amounts of solvent, and perform dilutions. These manipulations give the students a hetter understanding of the mole and concentratinn conceDts and also helo them to estimate these quantities. In the remaining parts of this experiment, students work with some "real world" solutions. One such solution contains 2 Tbsp of salt to 8 L of water and is used for boiling spaghetti. The students weigh one tahlespoon of salt and calculate the molarity of the final solution. Similarly, the molarity of sugar in a cup of coffee is also computed. Fmm the labels on the box of salt and the hag of sugar in the lab, students compute the price of a mole of sugar and of a mole of salt. Students also work with 5%commercial solutions of bleach, vinegar, and household ammonia. They calculate the molarity of each of these and explain why the molar concentrations differ. They also calculate the molarity of a window washing solution made by adding 100 mI. of the commercial ammonia to 3.9 L of water. Finally, the number of grams of ethylene glycol needed to Drenare an 8 M solution of antifreeze (nrntects a 16-L car radiator to 0°F) is calculated. The Treasure Hunt After discussing in lecture the occurrence and uses of the more common elements, an out-of-class assignment called "The Treasure Hunt" is eiven in which students are asked to examine the labels on a~'numherof household products to identifv the inoreanic comoonents. Various cateeories are specified, such as cleansers (soaps, detergents, bleaches, Volume GO
Number 12
December 1983
1039
scouring powders, bathroom, oven and drain cleaners), personal products (toothpastes, deodorants), food products (salt suhstitutes, meat tenderizers, soft drinks, iodized salt, and haking powder and soda), and home workshop products (rust removers, solder, fluxes, ant poison, and photographic chemicals).Each student must report the names and pertinent chemical symhok for all inorganic ingredients in a t least ten products distributed over a t least five of the suggested cate. gories. Brands with the most informative lahels are suggested to the class. This exercise in label reading forms the basis for discussing the common used in cleaning products and also for pointing out that many brands of the same item use identical active ingredients.
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Journal of Chemical Education
Literature Cited (1, Scuft. I..W.. Hi1l.J. W.Znhwmvrki. 1.. M . m d Metu. P.."(.hcm~al lnvortieationsfur rhanginq~imea,"3rd*d., H W ~ P W!hhhshlng ce..M ~ ~1980. ~ ~ ~ (21 .J,I~c. M. M., Ne~!erville..l I...l,~hnric~n.D.0.. and IVcm..l. I..:'L.rh~,rat~mry Manaal lor Chemmlry, Man and S,xiety;'2nd ed.. W H Saundem Ca.. Phllndelphin. 197a. (3, H ~ ~ J I ~ Y . V . v . ~ . . ~H d~ S I ~ Y .EC . . . T ~ and ~ ~ if" ~ i~n t ~ h e vLO^. oratory," H ~ ~ ' t~ ~ h EiCO.. i ~ ~~h ~ i ~~ ~~ ~~1978. ~ ~ p ~ ~ i ~ . (4) Irgolir. K., Perk. ]...and O'Tcmnw. R.."Fundamenialsof C h e m i ~ t win the Lahalow: hdod.. H ~ & now. ~ N~ ~ YWOP C ~ .1977. ~
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(51 Msnahsn. S.B.,"(:enersi Applied Chemistry: 2nd ed.. W ~ l l a r dGrant Press. Rmsti~n. 1982. pp. 454-459. (61 Stine. W. R.:'Applid Chemiatry."?nd ed.. Allyn and Bacon. Rosum. 1981. lap. 2S& 261. "71 J o ~ P . M M.,Johnston. . D O . . NottPwilla,d.J..end Wu
