Microscale (4-mL)a Macroscale (1000-mL)

50.030

40

50

60

70

Time / minfigure 3. The microscale extractor remains at a constant temperaturenear the boiling point of the solvent throughout the extraction. Themacroscale Soxhlet (with moderate insulation) extracts at a signifi-cantly cooler temperature and exhibits a periodic fluctuation intemperature coinciding with the rise and fall of the solvent level.

very near the boiling point of the solvent, whereas withoutextensive insulation, the sample temperature of extraction ofthe Soxhlet fluctuates with the rising and falling of the solventlevel. The 1000-mL Soxhlet (with a layer of aluminum foil

00

Qualitative Analysis in the Beginning Organic LaboratoryJames H. Cooley and Richard Vaughan Williams*Department of Chemistry, University of Idaho, Moscow, ID, 83844-2343; *williams@neon.chem.uidaho.edu

Simple questions from students are frequently provocativeenough to make us rethink our teaching methods. Such wasa question that came from a student during the beginningpart of an organic course. It was, "How do you know all thesethings?" Many of the textbooks of 25 years ago presentedmore of the methods by which the subject is studied (1).Organic chemistry, as it is presented in textbooks today, is acollection of facts originating from conclusions reached byinterpretation of data collected in some laboratory at sometime. Except for the description and interpretation of spectra,description of other data obtained in the laboratory is notfound. This approach adds to the students' perception thatorganic chemistry is an abstract subject. As an example, mostorganic texts start with a description of bonding and move onto discuss molecular structure. The structures are presentedas factual information to be remembered-and for all toomany students, just memorized.

A New ApproachWe have developed an approach to teaching the organic

laboratory course (2) which emphasizes the collection andi nterpretation of data in order to solve a problem. This approachprovides a more balanced introduction to organic chemistryand an answer to the question posed by our student. Onetopic which we include in our laboratory course, and which isvery popular with our students, is qualitative organic analysis.

as external insulation) extracted at temperatures substantiallybelow the boiling point of the solvent-as much as 15 coolerfor hexane (bp 68.7 C). This represents an advantage forthe microscale apparatus, since the extraction temperature canbe accurately set very close to the boiling point of the solventchosen.

ConclusionsThe microscale continuous hot solvent extractor com-

pares extremely well with traditional Soxhlet extractors whilereducing the solvent waste produced in a 300-mL extractionby 99%. The extractor can be made by an amateur glass-blower and has promise for use in the microscale lab as ateaching tool for extractions as well as introducing represen-tative sampling.

AcknowledgmentSpecial tanks to the Geneva, IL, Laboratory of Waste

Management, Inc. for the use of a variety of Soxhlet extractorsfor comparison.

Literature Cited1. Williamson, K. W. Macroscale andMicroscale Organic Experiments,

2nd ed.; D. C. Heath: Lexington, MA, 1994.

The debate over whether to include classical methods ofqualitative analysis in the laboratory course has been relativelyquiescent in this journal recently. However, two papers onthis topic appeared a few years ago (3, 4). The first claimedthat with the advent of a computer library of organic com-pounds attached to an IR instrument, students always got theunknown correct and learned very little from the experience(3). The second defended classical qualitative analysis as a goodway to learn organic chemistry (4). Our own, admittedlyli mited, poll suggests that at least a third of professors feel thatbecause of spectroscopy, classical "qual" is no longer needed.

In "qual" the student is exposed to many of the reactionsdiscussed in the lecture course. For most students this is avery positive experience, which reinforces their understandingof organic chemistry. All these reactions give highly visualand pleasing results such as a color change or formation of aprecipitate. Reactions covered in a lecture text, such as thereaction of potassium permanganate with an alkene or 2,4-dinitrophenylhydrazine with an aldehyde or ketone, arereviewed and performed in the laboratory. The standardtextbook presentation tends to treat each functional groupin isolation. In qual, the very different reactivities of the vari-ous functional groups are compared. This comparison of thereactivity of different functional groups strengthens thestudent's understanding of the subject. The shift in emphasisaway from synthesis experiments, where the objective is to

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In the Laboratory

obtain a product, to using reactions to deduce informationabout an unknown is usually a welcome change. Data suchas boiling points and melting points, as well as spectra, mustbe determined carefully in order for the student to justifyreaching a conclusion about the structure of the unknown.When formation of a derivative is required, students mustadapt a general procedure to a specific compound. Theyfrequently learn a great deal from such an experience. Forexample, when a derivative is required, we find that studentsgain a greater understanding of recrystallization and therelationship of purity to melting point. Finally, introductionof a very systematic and logical approach to determiningstructure is something students like. We consider qual to bean invaluable part of our organic chemistry course.

In classical qualitative analysis, as presented in Shriner,Fuson, Curtin, and Morrill (5) or Cheronis, Entrikin, andHodnett (6), the student is directed to identify the unknownfrom tables that list possible compounds. The tables areorganized to collect together compounds with a particularfunctional group and to index these compounds in order ofi ncreasing boiling point for liquids or increasing melting pointfor solids. To use these tables, the student must determinethe functional group that is present in the unknown and theunknown's boiling or melting point.

Since it is crucial that the boiling point or melting pointbe determined correctly, we advise students to repeat thedetermination of these properties until they are certain thatthe results can be reproduced. In an earlier experiment wei ntroduce IR spectroscopy as the best method for identify-i ng a functional group; in these experiments we introducesolubility and classification tests as a means of identifyingfunctional groups. We ask students to classify unknowns byusing solubility and classification tests before recording anyspectra. Students welcome the verification of results thatcomes from using both methods.

MethodThe First Experiment

We elected to introduce this systematic approach toqualitative analysis, but to limit the number of classes ofcompounds and to use only three experiments. In the firstexperiment the unknowns are limited to alkanes, alkenes,alkyl halides, primary and secondary alcohols, and ethers. Theprocedure followed by our students is summarized in FlowChart I. For tables, we refer students to the CRC Handbookof Tables for Organic Compound Identification (7). Solubilitytests introduced at this point are in water, ether, and con-centrated sulfuric acid. Water and ether serve to introducethe technique used in determining solubilities and help todistinguish a low-molecular-weight alcohol or ether from therest. Concentrated sulfuric acid distinguishes an alkane oralkyl halide (which are insoluble) from an alkene, alcohol,or ether (which are soluble). Classification tests include, forthe alkyl halide, the Beilstein test, formation of a precipitatewith ethanolrc silver nitrate or with sodium iodide in acetone;for the alkene-, - the Baeyer test with aqueous potassium per-manganate and decolorization of bromine in methylenechloride; and for the alcohol (primary or secondary) oxidationwith chromic acid. Because good classification tests specificfor the alkane or ether are not known, the presence of thesefunctional groups must be deduced from the solubility testin sulfuric acid, negative results on other classification tests,and eventually from IR and NMR spectra. The data studentscollect allow them to use the tables to select a few possibilities.While we recommend that proton and carbon NMR and IRspectra be used to confirm the identity of the unknown afterits identification from "wet tests", students are required todecide for themselves exactly what data to collect. Gradingis based not only on the right answer but also on the writtendiscussion the student makes by careful interpretation of the data

now,,-narr iFor Alkane, Alkene, Alkyl Halide, Alcohol, and Ether

"Only primary and secondary alcohols are used as unknowns (tertiary alcohols are, of course, not oxi-dized by chromic acid).

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that have been collected. A major aim of these experiments,emphasized in the grading scale, is that the student gain anddisplay understanding.

The Second ExperimentIn a second experiment the classes of compounds intro-

duced are aldehyde, amine, carboxylic acid, ester, ketone, andphenol. The procedure followed is summarized in Flow Charts

For Acid, Aldehyde, Amine, Ester, Ketone, and Phenol

II and III. In this experiment solubility tests in water, 5%hydrochloric acid, 5% sodium hydroxide, and 5% sodiumbicarbonate are introduced. To decide between weak andstrong acids and bases, the student is directed to test watersolutions with litmus or pH paper. These tests introduce thesolubility behavior of acidic and basic compounds, and moststudents are able to use them to decide among the variousfunctional groups without too much difficulty. Classification

tests introduced in this experiment include a 2,4-dinitrophenylhydrazine test for an aldehyde orketone, a Tollens test foran aldehyde, formationof CO 2 bubbles in the solubility test with sodiumbicarbonate for a carboxylic acid, Hinsberg andnitrous acid tests for an amine, ferric chloride andbromine water tests for a phenol, and hydroxy-lamine, followed by ferric chloride, for an ester.As in the previous experiment, students use boththe solubility and classification tests and boilingor melting point to identify the unknown.' Asbefore, following identification with "wet tests",the student is encouraged to confirm the identi-fication with IR and NMR spectra.

The Third ExperimentIn a third experiment, the student is given

an unknown belonging to one of the 11 classesof compounds introduced in the first two experi-ments. We ask the student not only to identifythis unknown, but also to select, prepare, and pu-rify by crystallization a solid derivative of it. Themelting point of the derivative is determined andcompared with that listed in the tables.

Flow Chart IIIFor Water-Insoluble Acid, Aldehyde, Amine, Ester, Ketone, and Phenol

Confirmatory tests for amines (Hinsberg and nitrous acid tests also distinguish be-tween primary, secondary, and tertiary amines), esters (saponification and ferrichydroxamic acid tests), and phenols (ferric chloride and bromine water tests) mayalso be run.

Discussion and Conclusions

The qual experiments are a big departurefrom earlier laboratory experiences. The studentis to develop a plan for "solving" the unknownby deciding what tests to run and how much datato collect to present a convincing argument tothe instructor in support of their structural as-signment. We find that students need time toreach an understanding of the experiment in ad-dition to enough time to complete the assignedtasks. We inform the students in the first periodhow many unknowns of each type they mustidentify in the scheduled time (up to seven three-hour laboratory periods). We allow them to workat their own pace and encourage them to iden-tify additional bonus compounds. At every stepthere is sufficient time to carry out confirmatorypositive tests on authentic samples (provided) ofeach class of compounds. We strongly encour-age students to carry out these additional posi-tive tests, as it is, of course, imperative that theyshould know what to look for in a positive test.In addition, we frequently adopt the followingapproach. Tests like the evolution of a gas whenan aqueous solution of sodium bicarbonate and ace-tic acid are mixed are easily interpreted. How-ever, the same test with a high-molecular-weightcarboxylic acid is much more difficult to inter-

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In the Laboratory

pret, and students invariably ask the instructor for help. Atthis point, the importance of side-by-side comparison is dem-onstrated for the entire class. Thereby, even students who nothave a particular class of unknown and are not motivated toexplore all tests with authentic samples are exposed to thewidest possible variety of positive tests. This series of experi-ments is a confidence builder for our students. They feel thatthey have enough time to complete the tasks assigned andthat they are learning something useful from each test.

In informal surveys conducted over a period of severalyears upon completion of the courses, the majority of studentsstate, without being prompted, that they thoroughly enjoyedthe qual and learned a great deal from it. Many consider itto have been one of their best educational experiences. Forthe past four years, one of us has taught a second-semesterorganic lab designed to meet the needs of our chemicalengineering majors. This lab meets only once per week forthree hours rather than the two three-hour lab meetings per weekfor our regular chemistry major sequence second-semesterlab. The first half of this lab is devoted to qual as describedabove. Many of the students in this lab resent that they arerequired to take "so much organic chemistry" and are notkindly disposed toward a three-hour lab with only one hourof credit. We frequently notice a considerable change in thesestudents as the lab progresses. They become very involvedin the "detective work" of qual and express, with some surprise,that they are really enjoying the lab and learning things thatthey consider valuable. They are subsequently much morereceptive to the remaining half of the course. Usually at leastone student per semester from these labs decides to changeto a double major of chemical engineering and chemistry or

CAUTION

even to become a chemistry major, often citing the lab asthe turning point in this decision. Similarly, many studentsin these labs have gone on to participate in undergraduateresearch with one of the authors. Again they cite their verypositive experience in the lab course, and particularly qual,as their reason for choosing to engage in research. In manylaboratory experiments, students race through procedures,submit a result to the instructor, and finish without a chanceto reflect on what has been done. We feel that the necessityof understanding these experiments has caused the very fa-vorable comments from our students.

Note1. A reviewer suggested that more classical experiments (e.g., the

i odoform test and ceric ammonium nitrate oxidation of alcohols) bei ncorporated. While this is perfectly feasible, we have deliberately sim-plified the classical qual scheme to make the concepts more accessibleand meaningful to the students. Certainly, at the discretion of the in-dividual instructor, other "wet tests" could be added or substituted.

Literature Cited1. Noller, C. R. Chemistry of Organic Compounds, 3rd ed.; Saunders:

Philadelphia, 1965; Chapter 4.2. Cooley, J. H. J. Chem. Educ. 1991, 67, 503.3. Zubrick, J. W. J. Chem. Educ. 1992, 69, 387.4. Ziegler, H. E. J. Chem. Educ. 1993, 70, 230.5. Shriner, R. L.; Fuson, R. C.; Curtin, D. Y.; Morrill, T C. Systematic

Identification of Organic Compounds, 6th ed.; Wiley: New York, 1979.6. Cheronis, N. D.; Entrikin, J. B.; Hodnett, E. M. Semimicro Quali-

tative Analysis, 3rd ed.; Wiley: New York, 1965.7. CRC Handbook of Tables for Organic Compound Identification;

Rappoport, Z., Compiler; CRC: Boca Raton, FL, 1967.

Experiments, laboratory exercises, lecture demonstrations, and other descriptions of the use of chemicals, apparatus, instruments,computers, and computer interfaces are presented in the Journal of Chemical Education as illustrative of new or improved ideasof concepts in chemistry instruction and are directed at qualified teachers. Although every effort is made to assure and encouragesafe practices and safe use of chemicals, the journal of Chemical Education cannot assume responsibility for uses made of itspublished materials. Many chemicals are hazardous. Precautions for the safe use of hazardous chemicals and directions fortheir proper disposal are described in the Material Safety Data Sheets and on the labels. We strongly urge all those planning touse materials from our pages to make choices and to develop procedures for laboratory and classroom safety in accordancewith local needs and situations.

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