A Learning-Cycle-Based Organic Chemistry Laboratory Program for Students in Dietetics William J. Mueller University of Wisconsin-Stout, Menomonie, WI 54751
Piagt't's theory of intellectual dr\.elopment and its implications for science teaching have recei\.ed considerable attention in recent years. From initial discusiions cvncerning developmental stages and the learning of chemistry ( I ), sevwaI change5 have evulwd in chemical educatiun, primarily in genvral chemistry 12,:). 4,.51.Onesuch change was the devrlupment of the "learning cycle" approach to laboratory pxpwiences ( f i t . This change has been implementrd in a ceneral chemistrv "oroeram . - ( 7 )and has a ~ o a r r n t l yl w n s u c cessful. Its application in anorganic ch&nistry~lahoratory program is the focus of this paper. An Overview of the Chemistry Sequence for Students in Dietetics and the Role of Organic Chemistry The overall goal of the chemistry sequence for students majoring in dietetics is an understanding of metaholism. At the University of Wisconsin-Stout, this goal must be achieved in a three-semester time span and is currently heing met by three one-semester courses: introductory chemistry, organic chemistry, and nutritional biochemistry. A recently completed extensive curriculum study of these courses has resulted in extensive revisions of each course with the net result heing the currently offered sequence. This sequence is unified in objectives and direction to the achievement of an understanding of metaholism. The introductory course in the sequence introduces atomic structure. hondine. solution ohenomena. and thermodvnamics (81.' ~ h organ;; k course introduces carbon compounds, properties of these compounds, and the important reactions of these compounds. Compounds important in metaholism are highlighted. The nutritional biochemistry course utilizes the concepts developed in the first two courses to present an overview of metabolic processes appropriate to the study of - nutrition. Within this framework particular attention was paid to the design of the organic chemistry course and its associated lahoratory. The course content differs markedly in coverage from that suggested for a one-year course ( 9 , l O ) .The focus of the course is narrow and centers on carbonyl group containing compounds (aldehydes, ketones, carhoxylic acids, and acid derivatives) as the most important. (This focus was used previously and successfully in the design of an organic chemistry course for dietitians ( l l ) . )The course design also incorporates many ideas concerning content and organization recenrly expressed by others (12) b; limiting student exposure to only a small nuniher of reaction mechanisms initially and t o onlv a select cross section of re~resentativereactions. The organic lahoratory course'is designed to serve as an effective complement to the specialized organic chemistry course. An understanding of the basic nature of organic comoounds is stressed and special attention is oaid to carbonvl containing compounds (more than one-fourth of the lab course deals with them). The learning. cycle is used as a . strategy in the design of experimtmts in urdt:r to promote l~arning.The lah then incorporates [he learning ubiectives of the speiialized organic chemistry course and theleaking cycle approach to experiment design.
382
Journal of Chemical Education
Design of the Laboratory Course The learning cycle approach to the design of lahoratory exoeriences involves a succession of stares. These stages are " an exploration stage, a concept introduction (invention) stage, and a concept application stage (7). In the exploration stage, observations and manipulations are carried out by the learner. The function of this stage is an accumulation of information. This information may he accumulated in a random manner or, as is the case when time limits are imoosed, in a more directed manner. After accumulating information, it is analyzed by the learner in an attempt to seek relationships and to generalize from these relationships. The development of these relationships by the learner concludes the concept introduction stage of the learning cycle. The final stage of the cycle is the application stage. The learner extends the basic conceots develooed in the concent introduction stage. A succeisful exteniim reinforces the validitv of the conceotsdevelooed hv the learner and Dromores concnued use of these conc&ts. In the organic chemistry laboratory course at UW-Stout. the learninicycle is compl&d through groups of experiments rather than throuah individual exoerimenrs. The safe handling of organic chkmicals and thegenerally long time spans needed for organic reactions almost precludes a completion of the learning cycle within a single three-hour lab period. Grouping of experiments to develop some specifically defined vet hroadlv based contents. however. seems to he a workable system in-which the learning cycle ban be completed. The following description of the course outlines this approach. The laboratory course is divided into four main groups or sections. Each section has a soecific conceot t o develop. and the experiments ale designed to facilitate that deve.lopment. 'l'he first section develops techniques for the proper handling of equipment and chemicals and appropriate methods for acauirine information. The second section develoos the relationship between structure and physical properties and the relationship between functional . groups . and chemical reactivity. Section three explores reaction types and connects reaction types to functional group characteristics through mechanisms. Finally, section four explores concepts related to energy and to reaction rate. The combination of these four sections and the conceots develoned within them serves to meet the overall objective of anLunderstanding of organic comoounds. A description of each of the four sections of the lab program follows.
-
Section I. Lab Techniques This section of the lab promam (the first three experiments) does not lend itself well ilearning cycle approach. A standard description of using equipment, making observations, and handline eauinment and chemicals is eiven. Exnerience in each of th;?se'faEets is acquired by the &dent a n i used in later experiments. Section 11. COm~oundTvoes .. Five experiments are included in this section. 'l'he exploration stage involves the determination 13f physical propertien
(hoiling points, polarities, and densities) for representatives of each tvne of oreanic n)mpound studied (alkanes, alkenes, alcohols; aldehydes, ketonis, and carboxylic acids). Simple chemical tests are also attempted with each of the representatives and results noted. Concepts are introduced by asking the student to draw various comparisons. (For example, the effect of hranchine on the boiline., noints of alkanes is illus. trated by runstrurtion of graphs wmpnring the Ix)iling puints of straight chain alkanes with the boiling pointsofsingly- and doubly.branched alkanes of the same size,. Van der Waals forces, dinole-dipole attraction, and hydrogen bonding are introduced as reasonable expl&ationsfor c~mparisonsthat are drawn between physical properties of various types of compounds. Chemical reactivity-structure relationships are developed by directly comparing the reactions of various types of compounds with selected reagents. (For example, sodium metal is shown to react with alcohols hut not with alkanes or alkenes.) "Functional eroun reactivitv" is stressed as the concept'to he learned.%. i;ahown that compounds with a narticular functional e r o u. ~ react in a manner that is different &om the reaction manner of compounds lacking that functional erouo. The conceot a~nlications t w e involves unknowns. ~ h student k is asked toidentify the compound types represented bv each of two unknowns. This is to he done on thk basis of physical and chemical properties. Information eathered from and concepts develooed in nrevious exneriments are synthesized into a solution of the problem, and a successful solution is demonstrated bv correctlv characterizine the unknowns.
-
Section 111. Reaction Tvoes ..
Five experiments are included in this section. Exploration involves carmine out a renresentative reaction for each reaction type inv&tGated (elimination, oxidation, esterification, and carhonyl group addition). Concept development involves an examination of the reaction mechanisms associated with these reactions. The importance of the stmcture and reactivity of the functional group is stressed. Concept application is again based on unknowns. Each student is given data sheets f i r two unknowns. These sheets contain information about the physical and chemical properties of the unknowns. The student must identifv the unknowns and then carrv out reactions of the types appropriate to the functional groups in are demonstrated hv the unknowns. Successful annlications .. successful reactions. Section IV. Reaction Characteristics
Two experiments are included in this section, one on reaction rates and the other on heats of reaction. Each experiment
incornorates ex~loration.concept develonment. and annlication in its design. The rates experiment ;tilizes the c l s c a l solvolysis of t-butyl chloride as the reaction investigated. Rates are determined for individual reactions that contain various concentrations of t-hutyl chloride. Others are run a t different temperatures. Rate constants are calculated and an activation energy is determined. The concept of the relationship between reaction rate and reactionmechanism is discussed. The concept application involves presenting a iustification based on rate data and activation enerev ... for a mechanism proposed for tht: s ~ l v ~ l y sreiictinn is studid. The heats of reaction eweriment utilizes acid-base reartions as the study system.-~xplorationinvolves the actual determination of the heats of reaction of various acid-base pairs. Concept development involves a discussion of reaction spontaneitv associated with heats of reaction. Application .. involves answers to questions probing the connections between spontaneity and heats of reaction. Success of the Program
Since the introduction of this lahoratorv nroeram in the fall semester 1979, an improvement in the &erstanding of the nature of organic compounds and of reactions has been noted by the author in the students participating in the lab program. The com~arisonis drawn between students from the orevious lab prog;am and the current program and is subjective. A more objective comparison can he drawn by noting the greater degree of success in biochemistry achieved by students participating in this new lab program. The students appear to have a better grounding in the fundamentals of organic chemistry and are thus able to grasp biochemistry more readily. In summary, then, the program appears to be successful and the choice of the learning cycle format appears to have been appropriate. Literature Cited
(5) Bmoks, David W., Scholz, John J, and Tipton, Thomas, J.. J. C ~ ME . ,707m \.",",.
(6) Karplus, M, et sl.,J. Research in Science Teaching, 14.169 (1977). (7) Ryan. Mary Ann,Rohinson,Donald,and Carmiehsel, J: W. Jr..J. CHeM. Enuc.,51. 642 (1980). (8) O n d u , Muti" 6 ,"Chemktry for H d t h kiencegtheFvstCnvsemtheSequenco," presentedattheannudmeefingofthe UniversilyofWisconainChemistryFaculties, University of Wisconsin-Perkside, Kenosha, W i n s i n , October, 1980. (9) American Chemiesl Soeiety Orgsnie Subcommitteeof theCurriculwn Comrnittee.J. CHEM. EDUC.,49,761 (1972). (10) American Chemiesl Soeiety Organic Subcommitteeofthe Curriculum Committee. J. CHEM EDUC.,53.25 (1976). (11) Mueller, William J., J. CHEM EDUC.,51,674 (1974). (12) Wheeler. Desmond, M. 8.. and Wheeler, Magaret M., J. CHEM. EnUC.,56. 464 (1979).
Volume 59
Number 5
May 1982
383
