GARY E. DUNKLEBERGER Carroll County Public Schoals
A Rotating Schedule for Teaching Basic Techniques with Minimum Equipment Andree Prigoda Reed 21 17 Bonnie Brae Avenue, Las Vegas. NV 89102
The necessity of laboratory experience for teaching and learning science is endorsed by the National Science Teachers Association. According to Linda Parez, the laboratory provides students with the opportunity to do science rather than to learn about science. "Direct 'hands-on' experiences are considered essential to the learning process especially for the vast maioritv of secondarv school students who have vet to master the most sophistkated and abstract reasoning patterns."' Today the cost of maintaininga laboratory with the necessary equipment is becoming a nightmare. The increasing demands to include information on environmental impact, applications, and career opportunities in a course are limiting the amount of time that can be allotted to laboratory experience. This invaluable experience is losing ground in the American classroom. T o offer individual laboratory experience with limited quantities of each type of equipment, for the past four years I have used a rotating laboratory schedule. Prior to this time, I was disnleased with the werformance of my students in the laboratoly. I also did not fLel that I was reaching the students when thev needed assistance. For example, I found that trying to teach the use of our eight DialA-Gram balances to a group of 32 students in one class period proved to be inefficient and not very effective. Each lab bench accommodated four students who shared one halance. One student a t each bench became proficient and the others were lost when the "leader" was absent. I also found students trying to master technique when emphasis should have been placed on the concept being demonstrated. Frustration resulted because many labs could not he completed within the allotted time. In an effort to solve these problems. I initiated the rotating schedule. On paper, the schedule appeared chaotic, but in reality each student was able to do each experiment without the time lost in sharing equipment. I n o longer had students who "leaned" on their classmates: each student was solely responsible for the completion of a laboratory exercise. Now each student had 50 minutes alone with a balance, and I had time to make sure each student was correctly learning a technique or understanding an important concept. Learning basic techniques is an integral but time-consuming aspect of each experiment. I have found that if my students concentrate on technique on an individualized basis
for two weeks, the remaining laboratory experiments can emphasize concept and refine technique. Also, because our school had a limited supply of specialized glassware and other equipment, this rotating schedule provides each student an-opportunity to learn basic scientific techniques on an individual basis. Each exercise includes a detailed description of objective, method, and student expectations. A brief report including data, calculations, and answers to questions is due at the beginning of class on the following day. T o reduce nervousness among students experiencing their first laboratory situation, no harmful chemicals are utilized during this introductory period while they are developing technique. The students are asked to pretend that they are using toxic substances and therefore strive for the utmost care and precaution. A general prelab for the entire class is given on the first day of the session. A typical schedule is outlined in the table. Bask Technlques and Procedures
The following sequence of laboratory exercises will demonstrate the use and value of the rotating schedule. First Week Exercise 1: Introducing the Balance (Bal A). The balance can be demonstrated to no more than eight students at a time where all can
see and receive individual instruction. This group receives undivided attention at the beginning of the class period (about 10 mi") in the care and use of the Dial-A-Gram balance. Showing the students the way to read the vernier is much more effective with a small group. Usually two examples of weighing an item are sufficient to allow students to proceed on their own. Each student in the group of Rotating Schedule for Two Weeks
Bench
Mon
Tue
1.2 3.4 5,6
Preiab
Bal A F 8D Liq A
7,8
1. 2 3. 4 5. 6 7. 8
tor
Entire Class
Glass
Be1 B
3b
38
Bal B
Liq B 3b
Liq B
3a
w~d
murs
Fri
Glass Bal A
Liq A
F&D Liq A
FBD Liq A
Bal A
Liq B 3b Bal B 3a
3a Liq B
Glass FB D
3b
Bal B
Glass Bal A Lab Test Entire Class
'
Klein. S. E.; Yager, R. E.; McCurdy, D. W. "The Laboratory is Vital in Science Instruction in the Secondary Schools"; NSTA: 1981. Volume 63
Number 12
December 1986
1079
eight weighs an item of his or her choosing as I oversee them and verify their readings. I then leave this group as they spend the remaining lab period weighing five items; they repeat the sequence of weighing two more times. They are instructed to fill a 250-mL eraduated beaker to a desienated mark with water..weigh. ~ emntv . . the beaker, and repeat the sequence two more times. Community w p plies: 8 Dial.A.(;ram hnlanres, 8 rapillnry ruhpa, R p~nnies,and weighing paper. Exercise 2: Measuring Liquids (Liq A). During the first 10 minutes of class, students in this group are instructed to identify certain pieces of equipment using their equipment charts, determine the difference between each graduation of selected glassware, observe a meniscus, and make practice readings estimating thelast digit. Once these introduetorv tasks are eamolete.. I make mvself available to thrm lo answer questims, check their prartrce resdmgr, and demonstrate the use of the pipet and buret. The students spend the remainrng time making various volumetric ineasurrments, rumparing readings of less accurate equipment with equipment of greater calibration, and practicing the use of the pipet and hulh. Community supplies: graduated cylinders, 50 mL and 250 mL; graduated pipets, 1mL, 5 mL, and 10 mL; nongraduated pipet, 10 mL; buret, 50 mL; pipet hulh. After the orelah session. the Exercise 3: Glass Bendine .. (Glossl. . students are self-iuffiuient in uring the hurner nnd performini the indiratrd glass manipulations. At s m e time during the aecund half of the period, I observe each student correctly insert a glass tube into a mhher stopper. Near the end of the class period eachstudent turns in and receives a written approval on the lab report for the glass bends. Community supplies: 4-8 burners, wire gauze, safety glasses, 8 rubber stopoers, 2-4 trianaular files, term towels, glass tuhina. .. .and 1dropper of glycerine. Exercise4: Filtration, Decantation, and the Use ofReagentBottles ( F & D).After the prelah session, students can fold filter paper, set up the apparatus, and wash the insoluble solid. They are to compare the separation of an insoluble solid from a soluble solid using the method of filtration and then decantation. During the second half of the class period, I observeeach student pour an "acid" from a reagent bottle. Community supplies: 1 jar of copper(I1) sulfate pentahydrate with dispensing spoon, 1jar of sand with dispensing spoon, filter paper, 8 ring stands, 8 iron rings, 8 rubber policemen, 2 acid reagent bottles. The teacher must first give undivided attention to Exercise 1and then to Exercise 2 using about the first 20 minutes of the class period. The remainder of the period the teacher is free to make observations, cheek and correct technique, and give assistance to those desiring help.
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S e c o n d Week Exercise 5: Using the Balance (Bol B). Additional practice using the balance is gained by determining the density of a solid and a liouid. The students are introduced to exnerimental error and percktnge error. The teacher can circulate amonethe students to make " surp they are taking correct reedings. Community rquipment: 4-11 rherrnmwters; 4-b metric rulers; 8 regular +
