Creating Excitement in the Chemistry Classroom Active Learning Strategies Jay H. Worrell University of South Florida, Tampa, FL 33620 I n t h e fall of 1991 we initiated a general chemistry course in which students are required to attend a weekly participation section (1).The class meets for one hour per week in addition to the regular three-hour lecture. It is not a traditional discussion section or auiz section. Students a r e graded S (satisfactory) or U (;nsatisfactory) exclusivelv on attendance and class oarticioation. The S will not increase their lecture grade, b;t a uAwillreduce it by one letter grade. The purpose ofthe Participation Section is to engage students in active learning, that promotes thinking, doing, problem solvine, and writing. We involve students in higher-order th&king t h a t uses analysis, synthesisof ideas and evaluation of results. Less emphasis is placed on dispensing information and more on developing student skills via active inquiry, cooperative learning, and peer teachine - .(2). What follows is a description ofa simple activity that has a profound impact on student ability to understand mass to mole and mole to mass calculations. I t reauires about 50 minutes of work a n d can be performed i n both small classes (-25 students) and larger lecture halls with minor modifications in the presentation format. I t is also a n ideal laboratory exercise. The Activity Students perform a double replacement reaction that produces a precipitate. They are asked to record their observations. Students m u s t then convert the reactant names to chemical formulas, calculate formula masses, ~ r e d i c what t the reaction is. balance i t and use it to oert o m mass to mole and mole mass calculations. ~ t u d l n t s are asked to describe in writing, a n experiment(s1 to confirm the correctness of their mass calculations. Finally, they are asked to corroborate the Law of Conservation of from their calculations.
c ass
Equipment and Chemicals Prepare a cart that contains test tube racks, 5-10 large test tubes (25 x 150) and reagents. Several reactants that give colorful results are listed in Table 1below. They are 0.1-0.5 M reagents stored in 500-mL squeeze bottles. Write the name, not the formula, of the contents on each container. A number of other reagent combinations also give precipitates.' Directions 1. Distribute a work sheet to each student. Have students call offnumbers, one to six in the order in which they sit, moving across or up and down the rows. Students having the same number belong to the same work gmup. The work group number defines which chemical reactants they will use. Groups of three are ideal. Have students gather in their gmups. -
'For example. Ag(l)and Po(ll)both produce wnite precipitates w th DMG. Each has a d fferenttenure.
Table 1. Summary of Reagents and Reactions for Active Learning group assume test test tube #B number tube #A contains contains excess 1
2
3
4 5
3.50 g silver(l)
nitrate 5.00 g lead(ll) nitrate 1.75 g nickel(l1) nitrate 2.25 g lead(ll) nitrate 4.50 g barium chloride
product(s)
potassium chromate sodium sulfide sodium dimethylglyoximatea potassium chromate sodium sulfate
'N~(CIH~N&)
Students are to examine solutions A and B and record their observations both before mixing and after mixing. Instmct students to introduce eaual volumes (1-2 mL) of the desired liquid reagents irltu atest tuhc. Next, they arc tu wntp iprcdirr, and currectlv hnlnnre thechemical rquation t h n r describes the renction they pperfnrmrd. Each student working in the group, is to calculate the mass (weight) of the products produced fmm their reaction. Let students figure out how to do this by asking questions of each other within the group. Students will calculate and record molecular weights and moles with differentnumbers of significant figures.Let them come to this realization when they summarme the work group's data. We assume a mass for the dissolved solid contained in test tube A. It is given on the student work sheet. Likewise,we tell students to assume that there is exactly enough B to completely convert all af Ato products. The Student Work Sheet Each student receives a copy of the work sheet given below. It provides students with directions and organizational insights a s emphasized in Tables 2 and 3 below. Your work group number corresponds to the reaction you will study. Discuss in your group how to complete the following sections, then do them. Record your obsewationr for each or your ralutions before and aRer mixina. There is more here than meets the eye, so be a careful obsewer You may see something that another member of your group may not see. Write a balanced chemical reaction that explains what happens when the contents of test tubes A and B are mixed. What type of reaction is this? Calculate the mass (weight) of produet(s) that formed in your reaction, using the weight given for your reactant A in Table 2. *At the beginning of each step, clearly write and state in words what you are eal~lating. Volume 69 Number 11 November 1992
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Table 3. Student Calculation Work Sheet
Table 2. Student Observation Work Sheet group assume test tube test tube #B number #A contains contains excess 3.50 g sllver(l) nitrate 5.00 g lead(ll) nitrate 1.75g nickel(l1) nitrate 2.25 g lead(il) nitrate 4.50 g barium chloride
1
2
3 4
5
potassium chromate sodium sulfide
product(s)
+ +
sodium dimethyl- + glyoximatea potassium + chromate sodium sulfate +
'N~(OHINS~
Perform your calculations on the back of this work sheet. My work plan is to complete the table of data requested in Table 3.
How muld you verify or confirm the result8 of your cnlcula. tmns? Exactly what would you have to do7 Demonstrate how the l a w nfConservationof Mans work for your reaction.
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T v D ~ Results c~~ The heart of this activity is getting students to understand and perform the most fundamental of general chemistry skills: .Can they write a compound's formula given the chemical name? .Can students calculate the formula weight (mass)for compounds? .Can they relate an observation to a chemical reaction? Can they predict the names and formulas for the products of a reaction? .Can they balance the reaction and then predict (calculate) the expected masses for the products? Much to our surprise, very few students could demonstrate a proficiency in these skills several days after the concents were uresented in a lecture format. Listening and pa'ssive abs&ption of lecture information may be one reason why so many students perform poorly in general chemistry. The formation of colored precipitates fascinated students. It was very obvious that a chemical reaction occurred. Attentive students noted that some precipitates were finely divided solids (PbSOJ; whereas, other solids had particles that were large and coarse (AgzCr04) and o t h e r s formed large particles t h a t tended to f l o a t (Ni(DMG)z). Several students noted that heat was released in the chromate precipitations.
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Journal of Chemical Education
group# reaction MW's #moles mass. o
+
aA
bB
+
d:
+
dD
+
Writing formulas for the reactants and products was a challenge for most. Some did not carefully read the names of their reagents and assumed that lead has a n oxidation state of four while others did not know the oxidation state for nickel. Once a balanced chemical equation was in hand, too many students incorrectly calculated the formula weight of the reactant(s1 or produd(s). The common error was the multiplication of the formula weight for the species by its stoichiometric coefficient in the balanced equation. This active learning exercise also works in a large lecture section. Distribute the student work sheets. The instructor can perform the reactions or preferably ask several students to assist. Grouus are assiened in clusters of 3-5 conveniently adjacent &dents. ~er?ormone reaction, and ask all students to uerform the same required calculato work for 10 or so minutes. tions. Allow student Then that answers be supplied to fill in the work sheet table. The instructor is to a d as a guide. There will be questions asked by students. Carry out several other reactions so that students can see the color of the precipitates and then assign one or two more of the reaction calculations to be comoleted out of class. For examule. have the left half of the rbom complete the data table ?or reaction 3 and have the rieht half do reaction 5. Trv it. The results will amaze you. The use of small groups ( 3 6 students), requiring students to interact with their peers in arriving a t a concurrent response, provides direction for the weak and reinforcement of principles for those assuming a leadership role in the group. Of the many, brief in-class activities we have uursued. this uarticular activitv met with the hiehest degree of student enthusiasm, personal satisfaction, and degree of accomplishment. This in-class activity focuses student attention on mastering important basic skills via an active learning urocess. It urovides better understanding and skill retention than passive instruction (2).
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Literature Cited 1. Femandee, J.E.; Worrell. J. H . '
Chpm.Educ.1991,68(71,551-562. 2. Bonwell.C.C.;Eison.J.A.ASHE-ERICH@herEdc666Ropo~No 1(1991),Wash. ington, DC; The George Washington Univemitx Sehml of Education and Human Development.
