Unusual Laboratory Practical Examinations for General1 Chemistry Robert Silberman, Samuel Day, Peter Jeffers, Kent Klanderman, M. Gail Phillips, and Arden Zipp S.U.N.Y. at Cortiand. Cortland, NY 13045 Althoueh chemists have often eiven laboratorv"oractical . examinations the most avid practkoners of this art form are biolopists. The usual chemistrv laboratorv wractical exam takes-the form of determining the ions in k i n k n o w n solution or the percent of some ion or element present i n a known sample, i n essence a qualitative or analysis prohlem.l.2 These are practical tasks that may test laboratory skills, hut there is some evidence to suggest that students can accomplish the deductive task without a complete understandine of the c h e m i ~ t r vIn . ~ an exhaustive analvsis of the quantiitive type of laboratory practical pickerin2 lists several ~otentiallvserious ~ r o b l e m with s auantitative titration-type practical examinations. One wav to deal with these difficulties is to set un a laboratory-examination that involves a variety of tasks and types of questions. Our colleagues in biology are old hands a t practical exams and have attempted to vary the kinds of questions they ask on them. Their questions take the following forms: 1. Prepare a gram stain. 2.
Identify the structure indicated.
3. What is happening at the wave labeled C in the EKG?
The first question is similar to the chemist's practical taskoriented question. The second question asks for the recall and recognition of something observed in the lahoratory, and the third question asks for the interpretation of data, a more comnlex thinkine skill. What is missine in both of these approaches is a test of a skill that was o&inally termed He attempted to laboratory resourcefulness by H. A. test the ability to solve simple laboratory problems. His tasks were of the following sort: ~
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1. Setup: Three unequal size bottles, one filled with water, sand, 2.
scales, no weights. Directions: Divide the water into thirds. Setup: A large bucket of water, fastened down, bottle and rubber tubing. Directions: Fill the bottle with water from the bucket without moving the bottle.
In Webb's examination, problem solving, a more complex and difficult skill than following directions or recalling a particular piece of information, is being tested. The laboratory goal for our general chemistry course is to show the relationship between experimental science and the concepts developed from experimentation. We have tried to use laboratory exercises that encourage experimentation, such as learning cycle lahoratory experiments, which stress careful observation, clarify concepts, and give meaning to theinformation in the textbooks and lectures. A secondarv goal is to develop note taking, observation, and lahoratory manipulative skills. We decided to test the development of
622
Journal of Chemical Education
these skills with lahoratory practical exams that differed from the traditional ones. Our examination questions fell into the six categories below:
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1. Simole lahoratorv skills 2. Laboratory resourcefulness 3. Observation and collection of data ~~~~~~
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The actual exams took place in the lahoratory and were a combination of written examination questions and task-oriented questions. An examination usually consisted of between five and ten questions. The exact makeup depended on each instructor. The physical setup of the examination involved setting up stations around the laboratory with a question or problem a t each station. The exams were set up before the students entered the laboratory. In order to avoid bottlenecks we set up several stations with the same problem when we thought a problem would take students more time than the average question. Students moved from station to station a t their own pace. Some tasks took as long as 10-15 min, some only a minute or two. At the beginning of the semester students were encouraged to keep complete and detailed notes and observations in their notebooks. They were also told that the practical examination would involve using material that should be in their laboratory notebooks if they had taken careful notes. Studenti w r e n s k d to bring their lahoratory notelxwks to Inl~umturywnh the undtrirnnding that the notebooks would he used during the examination. One examination was given each semester, and i t was counted as the eauivalent of two laboratorv renorts. The examination usuaily lasted between one andtwo'hours. We do not usuallv set a strict time limit. It is our feeline that for exams of this type students need plenty of time i o think. Allowing students to use their laboratory notebooks for the examination seemed to be an excellent way to encourage students to keep an organized useful notebook, rather than the scribbled jumble of seemingly random information that Presented at The American Chemical Society Spring National meeting, April 1986, as part of the symposium on Creative Examinations sponsored by the Chemical Education Division. 'Jones. M. M. J Chem. Educ. 1977, 54.178. Pickering, M.; Monts, D. L. J. Chem. Edoc. 1982, 59, 1032. Pickering. M. J. College Sci. Teach. 1979, 8, 178. Webb, H. A. School Sci. Math. 1922, 22,259-267.
we have so often found. It reinforced t h e message t h a t laboratory notebooks could actually h e useful several weeks after t h e d a t a were collected. There are readily observable benefits associated with our laboratory tests. S t u d e n t s reviewed t h e semester's lahoratory program rather t h a n forgetting about t h e laboratory experiment a s soon a s i t was done, a n d they k e p t much better laboratorv notebooks. Our exams also ~ o i n t e do u t to our students t h a t creative problem solving Gas a valued skill i n t h e lahoratorv. Finallv t h e v encouraaed us. as instructors. t o examine o u r goals a n d ohjkctives f o i t h e laboratory part of our general chemistry course. Since we have n o teaching assistants a t Cortland a n d each laboratory is taught by a regular faculty member, each instructor in t h e course wrote h i s h e r own exams, s o the style and emphasis differed from one section to another. Therefore, i t is difficult to evaluate t h e difficulty of each examination question objectively. Some sample examination questions t h a t were used over t h e course of several semesters a r e shown below.
Application of Concepts
Sample Examlnatlon Questions
Data Acquisition and interpretation 1. The test tubes at this station each contain 1.00 g of material.
Simple Laboratory Skills 1. Read the level of the liquid in the huret 2. How much uill lN.000 of thrw ubjrct, wrigh" What is the arrur in "our emmafe7 Setup: nn ohirer ncxl to the balance 3. S11ppc~sey0u hnw I ~ ~ , ~ ~ c u I ) ~ ~ Y of Ps &OH ~ ~ I (MW401. u~:o~F All w u have are \ ~ l u n l ( . l l fla4ki. i~ ~)iprtsand 3 1. trf 1 2 l4 NaOH d u u m The sc,lutians musr mnge from u.01 M tuO.1 1 1 and yuu need ?.XI m1.d each solution. Explnin how you uuuld prepare each solution, and show any calculations you used
Laboratory Resourcefulness 1. Will the white ball float in the liquid in bottle A? Describe your experiment. Materials available at the setup: assorted small graduated flasks and cylinders, a small-mouth bottle of liquid A. a balance. strine. and a ruler. No container has an ooenine b& enoueh far theball to fit in. The halls were made ofhifferent plaitlcr ahout a n mch in dinmerrr with densities bttucen 0.8 and 1 3 . The liquld were common Inhorntor) sulvt.nts such as alcohol or triehloroethylene. 2. Dprermine which of thr measuring devices is the most prerw. 1leasurmg devues used: araduatrd rylhder. buret, pipet, and a small graduated Erlenmeyer flask ~
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3. In the experiment, "A Question Of Magic", the disappearance of the blue color was due to the following reaction: iodine starch complex reducing agent 1- (colorless). The reagents necessary to produce the blue complex are at this station. Determine which ofthe unknown solutions W,X, and Z is (are) reducing agents. 4 . Find rhr den.;~rvo i mrrd shot ar A funcrion of the numher of shot i w d . (;raphwallg d i & w the wsulrs, nnd interpret them.
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1. Develop a classification method so that the people in this room
can be classified into one of five possible unique groups. 2. Determine the density of unooooed ooworn. . .. . . :1 Suppose y w were in charge of a laborauq and werp giwn the ta-k ofdeterminmp the conerntr~tionof 1U0 samplcsof potasaium dic hrcmatc. a wlluw solution. You haw availahlc sdid potassium dichromate and standard laboratory equipment. How would you accomplish the task?
Carefully determine the solubility of each material expressed in g salute1100 g water. 2. 'l'oobicrvr theeffert o f t e m p w ~ t u r rfind , the reaction time for 10 ml. .\ and 10 mL B at rwpmldffermt '1"s asaiywd by yc,ur m1rurrc.r ( l U , 15. 'LO. ' 5 , :10. 35 'C). Find thr svm:iic rate constant for each temperature and fill in values on the chart on the blackboard. The Arrhenius equation can be used to find the activation energy of the reaction. log k = log A - E.12.3RT How can the equation for a straight line be fitted to this equation? Use the class data to plot the appropriate variables, find the slope of the straight line, and then the activation energy for the clock reaction. Hand in your plot and the value for E,.
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O b ~ e ~ a tand i ~ Data n ~ Collection 1. Find a linear relationship between the objects at this setup.
The objects: several solid cylinders of aluminum with assorted measuring devices. 2. The four bottles contain an acid, a base, a salt, and water. Which is which? The reagents available are: blue litmus, silver nitrate solution, and phenolphthalein.
Laboratory Note-Taking Skills 1. List one set of data you obtained in the experiment on variables. Be sure the information is correctly labeled. 2. Answer from your notebook: (a) In the classification experiment, what is the effect of solution # 2 on the test paper? What is the effect of mixing solution # 5 and sodium carbonate? (b) In the Magic and Science of Chemistry experiment, what was the order of sequence of colors sought? 3. Describe the observations which you made for one of the following experiments. Write an equation that represents your observation. (a) Dilute nitric acid was added to potassium dichromatesolution. (b) Conc. HCI was added to a solution of eobalt(I1) nitrate. (c) HCI was added to a mixture of SbCls in water. After the addition of acid water was added again.
Responsibility Experiments, laboratory exercises, lecture demonstrations, and other descriptions of the use of chemicals, apparatus. and instruments are presented in this Journal as illustrative of new, novel, or improved ideas or concepts in chemistry instruction and are directed at qualified teachers. Although every effort is made to assure and encourage safe practices and safe use of chemicals, the Journal of Chemical Education cannot assume responsibility for uses made of its published materials. We strongly urge all those planning to use materialsfrom our pages to make choices and to develop procedures for laboratory and classroom safety in accordance with local needs and situations.
Volume 64
Number 7
July 1987
823
