LABORATORY PERFORMANCE TESTS IN CHEMISTRY B. CLIFFORD HENDRICKS University of Nebraska, Lincoln, Nebraska
INTRODUCTION
The traditional type of examination has been found to have negligible value for assessing the effect of laboratory work upon a chemistry education, Paper and pencil tests1 do measure knowledge of laboratorv skills and ~roceduresbut have not vet been validated as measures of laboratory performance. Studies2. a indicate that performance or practice tests do reveal that students who had individual laboratory training have skills and abilities which were not exhibited by students whose course in chemistry did not provide laboratory practice. These findings of Horton and Burrows, however, have not been used by teachers of science. This 1% of teaching practice behind demonstrated validity of an examination form is, in all probability, due $0 the impracticability of the method of administering the performance tests. The following occur to the writer as reasons that Performance tests have not come into use by teachers in service: 1. The testsfonnulated by the investigators were individual tests requiring one proctor for each student examined. 2, ~h~~~ is a hazard of "caw-over" from one student to the next in sequence when there is a time interval between tests. 3. To reduce "carry-over" different items would be used on late comers. This has three liabilities: increased burden of test constmction, decreased comparability of student r e sponses, and increased demands for perfolmance equipment. 4. Rating by score card is not desirably objective. 5. Providing performance equipment adds to the administrative burden of performance tests. This falls upon both storeroom personnel and teaching staff. 6. m n equipment and supplies are used in a test's administration there is always a time requirement for "clean-up'' and "put-away." 7. It is more difficult to Prepare acceptable items B. CLIFFORD, J. CHEH. EDUC., 22.544 (1945). HOETON, R. E., "Me~surableOutcome~of Individud Labortory Work in High School Chemistry" Bur. Pub. Teachers' College, New York, 1928. Bmows, J. AUSTIN, Unpublished Monograph. "Methods of Laboratory Instruction," Oklshoma A. & M. College, Stillwater, Oklahoma (1936). 1 HENDRICKS,
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requiring performance with equipment than those aiking for remembering a n d understanding. 8. It is easier in such tests for a student to get suggestive leads from his neighbors than in pencil and paper tests. .4 number of criticisms listed above may be some-,hat alleviated. performance tests may be constmcted for administration to groups instead of individuals. R~~~~~~~~ may be required by the student's entryupon his individual score card rather than upon a score card in the hands of the proctor. The items may be so formulated that use is made of standard desk equipment rather than special apparatus. of chemicals and of equipment items re~ h minimum , quired may be drawn from the storeroom by the student the day before the test. ~h~ uclean-upu and away" may he incorporated into the test as scorable items. An approach to privacy of the examinee may be attained by using the two desk drawers placed upon either side as screens. (An excuse, to the student, for this arrangement may be, that your burner flame may be ,teadied as you bend the glass.) WHAT OUTCOMES THE TEST SHOULD MEASURE
Horton4 has listed the measurable outcomes of laboratory work as: Ability to manipulate apparatus, to make experimentation involving apparatus, and to solve perplexities or projects involving the use of chemical facts in laboratory situations. Another phrasing' for measurable aims of laboratory practice says: "The item is to require the expression of chemistry in terms of chemicals or equipment. Or concrete chemical substances and equipment are to be required to have chemical meanings." Thus outcomes or aims of laboratory work appear to be related to apparatus, chemicals, and processes involving equipment and chemicals. It is in order,. then, to ask, "What are the techniques and processes of which general chemistry students should have knowledge and skill?n Books on chemical engineering5 organize their content around what they call unit processes. Are these unit processes of engineering chemistry suggestive for compiling a list of technique objectives for general chemistry? These unit processes are, generally, phys' H o R ~ NR. , E., 100. cit., p. 100. W. L., AND W. L. MCCABE,"Elements of Chemical Engineering,"McGraw-Hill Co., Ine., New York, 1931.
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ber units: gas on solids, gas on liquid, liquid on solid. (3) Absorption units: solid for gas or vapor, liquid for gas or vapor. (4) Condenser units for: distillation, *sublimation. ASAMPLETEST
W u h Bottle
ical processes, but they are, nevertheless, processes that produce results that have chemical meanings. Manuals6 devoted to standardized techniques, are another helpful source of listings of apparatus with special reference to correct manipulation. From these sources and current laboratory manuals for general chemistry the following equipment and process units have been compiled after checking with an unpublished list prepared a t the 1941 Univelsity of Chicago Summer Work~hop.~ REFERENCE LIST OF TECHNIQUES. PROCESSES. AND EQUIPMENT UNITS
If skill in the recognition, use, and understanding of the above-listed processes and units constitutes an acceptable evidence of achievement in the laboratory, the construction of a test becomes a matter of selecting adequate samples of such units or processes for identification, use, and interpretation. That which follows is submitted as an illustration of how to construct a performance test utilizing some of the suggestions, previously made, for improving the practicality of laboratory performance tests. In this test the principal problem is: "A study of the decomposition of starch." The problem is broken down into five parts, each so designed as to test as many elements of laboratory technique and skill as possible in a minimum of time. These parts are: 1. 2. 3. 4. 5.
Glass fabrication. Improvement of an incorrect setup. Generation, washing, collecting, and testing gases. Disassembly of the apparatus used. Quantitative reading of: volumes, length, and weight.
For Part 1 the student has been provided with a 35cm. piece of glass tubing, a file, Bunsen burner, wingtop, and metric rule. The requirement is: prepare a 5- X 15-cm. right-angle bend and a 15-cm. straight delivery tube. The proctor rises the following score card. Credit one point for each item performed acceptably.
Unit Processes: (1) Crushing and grinding. (2) Crystallization. (3) Decanting. (4) Dissolving. (5) Distilling. (6) Drying by heating or desiccation. (7) Evaporation by aid of vacuum. (8) Filtering by 1. Planning, i. e., bend made before cut. gravity or suction. (9) Gas techniques: adsorption, 2. Use of the file and method of making the break. collection. (10) Mixing. (11) Sieving (size separation). (12) Sublimation. 3. Correct use of the wing-top. Miscellanewus Techniques: (1) Glass work: fabrica4. Turning the glass tube as it was heated. 5. Bend, 90 degrees and in one plane. tion, repair. (2) Heat sources: Bunsen burner, blast 6. Tube ends fire-polished. lamp. (3) Reagents: care, dispensing. (4) Rubber use: stoppers, tubing. (5) Waste materials: removal, For Part 2, provide a diagram labeled "Wash bottle disposal. (6) Safety procedures: concentrated sulfor removing a gas from a gas mixture." (See figure.) furic in water, proper catalyst (not charcoal) in potasIt is required that the student improve the setup by sium chlorate, concentrated sulfuric on chloride not chlorate, sodium peroxide in cold water, hydrogen gas use of equipment and supplies previously secured for ignition, ammonium nitrate decomposition, absorption this test. The score suggested for this part is: of poisonous chlorine or hydrogen sulfide, detecting 1. Increase limewater depth. odors, tasting (?), "foolproof" generators. 2. Change the generator unit to the 5- X 15-cm. Glass Tube Units (Student-made for setups): (1) delivery tube, B. Equal arm, 5-cm. riiht-angle. (2) Unequal arm, right3. Substitute a two-holed for the three-holed stopper angle: 2.5 X 10 cm., 5 X 15 cm. '(3) Unequal arm, (or properly plug the third hole). 5 X 15 cm., l35degree angle. (4) Open straight tube, 4. See that glass tube ends extend through stopper 15 cm. (5) Stirring rod, 15 cm. (6) Pipet tip, 5 cm. holes. Process Apparatus Units: (1) Gas or vapor generaFor Part 3 the directions would require that the tor, from: liauid and solid, solids. (2) Reaction chamimproved unit for Part 2 be connected to additional s Sp~norre,N. G., "Basic Laboratory Practice," Chemical equipment for collecting and testing gases that may be Publishing Co., Ino., Brooklyn, 1940. generated from a heated mixture of sand and starch. ~ADMIS, C. S., J. CAEM.EDUC., 19,267 (1942).
The gases are to he washed by passage through the bottle prepared in Part 2. The student has previously been alerted to needed equipment for such setups. The starch-sand mixture is issued to him by the proctor. The student is told that he will be rated on both setup and meaning he gets from the results. Score card for this setup may include:
4. Weight of a glass stopper balanced on a triplebeam balance.
In preparing for this test the student would he asked to inventory his desk equipment, the last laboratory day before the examination, to make sure he had a hard glass test tube with a one-hole stopper to fit, two wide-mouthed bottles with two- and three-hole stoppers 1. Use of 135-degree bend as part of delivery tube to fit, a complete set of "student-made glass tube units" (see paragraph three under section entitled "Referto pneumatic trough. 2. Use of 15- X 2l/,-cm. right-angled bend a t end ence.. .Equipment Units"), a 20-cm. length of rubber tubing, wing-top, Bunsen burner and tubing, metric of delivery tube. 3. Glass ends "butted" within rubber connections. rule, pneumatic trough and bridge, glass plates, deflagration spoon, matches, and towel. The proctor 4. Proper placement of the trough bridge. will make sure there is a 35-em. length of glass tubing, 5. Collecting bottle free from air. and proper supply of filtered limewater and sand6. Proper heating of the generator. starch mixture so that there may be no delay in their As an interpretation of the experiment, the following issue to the students a t the first of the examination might be required: period. On the day of the examination the student would 1. What does the change in the wash bottle inrepair to his desk as usual a t an assigned hour. Unless: dicate? his time to read the instruments in Part 5 interferes 2. What property made the gas collectable? 3. If the gas collected burns what property of its he would begin a t once upon Part 1 after receiving a: direction sheet, the glass tubing, and sand-starch constituents is indicated? mixture. His direction sheet carries the form for reis in the decomposition 4. What possible third gas port on parts 4 and 5. The proctor keeps his score products? record upon a master sheet and transfers that record to 5. What may the residue in the generator he? 6. Explain four or more decomposition prod- the student sheet after the test. ucts from starch, a three-constituent comDISCUSSION AND CONCLUSION pound. The direction for Part 4 would have the apparatus The writer has found that the requirements set forth used in Part 3 taken apart and thoroughly cleaned in the tests just described may be met by a student in a before storage in the desk drawers. The score items period of one hour. A single assistant can proctor of this performance might be: six students and rate them for the ten items subject to 1. Use of towel as protection while removing glass observational scoring. This means that in a threehour period, per usual laboratory session, a given assistfrom rubber. 2. Water-wash hut not inside drying of insides of the ant can get a set of performance test scores for all individuals of his 18-student laboratory section. bottles. 3. Use of a deflagrating spoon handle or glass tube in This represents an allotment of from 3 to 6 per cent of total laboratory time per semester for laboratory testing removing residue from the generator. 4. Grouping pieces as they are put into the drawer compared to the usual 12 to 18 per cent of his lecture time so allotted. for storage. Experienced teachers will have little difficulty in The reading called for in Part 5 would be made by using some such pattern in setting up other problems to the student by a time given him a t the first of the test these or other aspects of laboratory performance. period. By so doing one set of samples could be made They also may wish to prepare two or more comparable to serve the whole group. Scoring on these readings forms for a given problem to use with examinee groups might give two units upon each: one for the correct which come a t different times for the test. The writer whole number and the other for the correct decimal would, above all, emphasize the necessity of persistent unit value. The measurements are: experimentation within the teaching program. This he believes to be the pragmatic means of improving the 1. Volume of mercury in an eudiometer tube. quality of the teaching services to the students in the 2. Volume of transparent liquid in a buret. college chemistry classes. 3. The length of a wire on a meter stick.
