going beyond. going further
edited by N. H. ETTINGER George Washington High School Bustleton Ave. and Verree Road Philadelphia. PA 19116
Student-Designed Labs Rick Broniec J. I. Case High School. 7345 Washington Ave., Racine, WI 53406
Like many instructors in secondary chemical education, I have become disenchanted with student responses to experiments found in laboratory manuals. Great effort cannot get even second-year chemistry students really to think about their lab work and relate it to lecture material. As a result, labs can become simple "cookbook" exercises that promote little, if any, critical thinking. In an effort to overcome this deficiency, I have employed an approach that has proved to be very successful: I assign each student a laboratory problem, give them a list of available equipment, and have them design their own experimental procedure. Each student works independently and, of course, must have hisfher procedure checked by the instructor before doing the experiment. The students theu perform their self-designed experiments in the lab to see how well their procedures work. Success of anexperiment is measured primarily by the student's percent error as compared to a handbook value for the quantity they have been assigned to measure. Unsuccessful experiments can then be redesigned and performed again, if time permits. Student response t o this exercise has been gratifying. They really seem to enjoy the opportunity and feel i t is worthwhile for a number of reasons. First, they are forced to research their problems thoroughly in various lab books and texts kept in the school library or on classroom shelves (1-6). In so doing, they often become familiar with more than one technique that may be used to perform their particular experiment, and they have to evaluate suggested techniques to choose the most appropriate. Second, they learn the value of controlling as many variables as possible as well as how variables are controlled. And, finally, they really begin to understand and appreciate the logical progression of steps that can lead to a successful experiment. Other advantages of this approach include a rebirth of student ingenuity that sometimes boggles the mind! (A student once brought in an aquarium pump t o pump oxygen into his candle "combustion chamber". . .hut that is another story.) And perhaps most importantly, independent and creative thinking is fostered since each student works without benefit of or reliance on a lah partner! This type of activity can he completed in about the same time as a "cookbook" lab, but additional time is needed previous t o the experiment to discuss such factors as lab technique, available equipment, etc. Disadvantages include greater preparation time for the instructor (to set up as many as 25 different labs per class), as well as the problem of dividing your precious lab time between 25 or so different experiments a t a time. Safety could also he a problem unless care is taken to choose the appropriate type of activity. I use this approach a t least once a year in aunit on thermo-
dynamics for second-year students who have been exposed to a number of lab techniques previously. Each student is assigned a heat of reaction to measure usine calorimetrv. ~ a l & m e t r y lends itself well to student self->esigned la6s because there are many different quantities that can be measured with relative accuracy in abigh school laboratory (insuring that each student receives a different problem). For example, the heat of fusion of water, the heat of solution of various salts, the heat of acid-base neutralizations, the heat capacity of metals, or even the heat of combustion of candle wax all have worked well in the past. Results with less than 5%error can he achieved with simole coffee-cun calorimeters (for procedures other than he& of comb&tion). The maioritv . . of these auantities can he measured more than once in a one-hour labberiod, improving both accuracy and precision. Chemistry instmctors are always looking for research project ideas that can be successfully completed by a highschool student using techniques and equipment available in a high school laboratory. Another suggested application of this "self-designed lab" approach, theu, might be to create science fair chemistry research projects. A well-thought-out, self-desiened exoeriment could he e x ~ a n d e dinto a more extensive science project with relative ease. Calorimetry works particularly well as a project for several reasons. First, fairly accurate calorimetric measurements can be made using the unsophisticated lab equipment available to most high schools. Second, there are, as previously stated, many quantities that can be studied. Finally, a wide range of enthalpy data has been reported in various handbooks (7,8) for comparison and analysis of lab results. As an example, a student could initiate a study of the heat of reaction for an acid-base neutralization a t varying concentrations. Or a cornoarison of heats of solution of a salt a t different temperatures could be carried out. One student recently undertook a study of how the heat of a sulfuric acid-sodium hydroxide neutralization varied with the molar concentration of H7SOa . . and NaOH. He simolv mixed together 100 mL of each solution in an insulated styrofoam cup and measured the temperature changes associated with the reactions. He varied-the concentr&ions of the acid and hase in a systematic manner in an effort to test his hypothesis that "the higher the concentration of acidand hase, the higher the heat of reaction". Not unexpectedly, his hypothesis was supported by the data! Though this student's work was not turned into a full-blown research proiect. it could have been with minimal effort. noth her student conducted a study of the heats of combustion of various alcohols to see if there was any relationship between the alcohol's formula and its enthalpy of combustion. She "discovered" the organic chemistry principle Volume 64
Number 11 November 1987
981
that the heat of combustion of an alcohol is directly related to the number of carbons in its formula. There is, of course, a large margin of error in calculating heats of combustions using tin-can calorimeters due to the loss of heat through conduction and convection. As a result, this student's absolute values were off quite a bit. Neverthea trend in her data less, she was able to recognize that compared well qualitatively, if not quantitatively, with expected results! The possibilities for research projects this nature are limited only by your students' creativity and drive! Having students design their own experimental procedures and projects certainly does not guarantee student understanding of laboratory principles, but it does work to expand student awareness of the value of performing well-
962
Journal of Chemical Education
designed and carefully thought-out experimental work. I feel that this approach works and is well worth the effort! ~ l t ~cried ~ ~ t ~ ~ e 6th 4.; . , L.: ~ ~ ~ ~E. J.: i ~staniUki, ~ k iC. ,L chemical sunders: ~ h i ~ a d d p h i1985. i. S1mimki.E.J.: W d w . W.C.;M&ertm.W.L. ChemicalPn'neipleaintbLoborotory, 4th ed.; Saunden: Philadolphla, 1985. B ~T. L.:~L ~ M, S YH., E. chemistry-the c e n t d seienee. 2nd ed.; ~ r e n t i c e ~ a i l : Englewaad Cliffs, NJ, 1981. Nelson, J. H ; I'emp, K. C. L.bor.lary Erpsrimonla for Chemistry-the Cenlrol scimeo, 2nd ad.: ~ m t i c e ~ d~nglewoad l: cliffs.NJ, 1981. Parry, R. W.: Bassow. H.; Menill. P.:Tdlefscn, R.L. Ch~mi~fry-Experim~nlolFoundolions. 3rd ed.: P r e n t i c c H d : E n g l e w d Cliffs. NJ, 1982. M ~ , ~ ~P.I:Iparry, , R. w.:Tellofsen. R. L.; B ~H. ~ ~ ~~Manual ~ for b chomis~ ,~ ~ try-~xpsrimmto~~oundotions.3rded.;~rentice-~si~: E ~ ~ I ~ W ~ ~ C1982. I ~ ~ ~ S , N J , Lange,N.A.Langa'a Handbook ofchamiatry. 1Mhed.: McGrau-Hill: NewYark, 1967. Handbwh of Chemistry and Physics, 51st ed.; Chemiesl Rubber Co.: Cl8ueland, OH. IWO-'~I.
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