Hubert N. Alyea Princeton University Princeton, N. J. 08540
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Microchemistry Projected (TOPS)
Projection of micro-experiments is a new proposals to be suggested by the student during a single technique which involves each student in laboratory experiment; the displacement of Cu2+by Fe is used as an work, yet fits the budget of everyclassroom in the world. example. (5) Teacher Manual: General instructions Grams are used instead of kilograms; an entire year of to the teacher; special instructions for the CuZ+ Fe experiment; answers expected from the student. (6) experiments costs five dollars. Chemical reactions are Projectors: two homemade projectors; details for makprojected in full color on the wall; beakers appear a ing an inexpensive ($0.50) lensless projector; commermeter high; bubbles of gas and droplets of liquid appear as big as baseballs; noxious gases, smokes, and explocial projectors. sions are of micro-dimensions. Apparatus is immediChemicals ately ready to use or to lay away. I n fact, experiments using the UNICELL described below could he Of the chemicals listed in the TOPS seriesZthe followcarried out individually by 1000 students in a lecture ing suffice for the beginning teacher. Dangerous chemihall. This article describes the technique, summarizing cals such as concentrated acids or flammable substances a monthly series which has appeared in THIS JOURNAL have been omitted. The original numbering system in since 1962.' I t includes the following information. the TOPS series has been retained in the list below. (1) Chemicals: Sixty-one reagents; the dangerous Store the reagents in 50-ml square glass or plastic hotones have been omitted. (2) The UNICELL: a simple tles. apparatus used for performing several hundred experiments. (3) Picture-book experiments: nine demonstraLiauids tions illustrating the versatility of the UNICELL. (4) 6M solutions whenever possible, in bottles with dropper caps. Student Workbook:questions to be answered and research
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ALYEA,H. N., "Tested Overhead Projection Series (TOPS)," (3rd Ed.), ChemicalEducation Puhlishimg Co., Easton, Pa., 1967. A reprint of all TOPS articles in TEIS JOURNAL from 1962 to June, 1967, available from the Chemical Education Publishing Ca., Easton, Pa., $3.50. ' J. CEEM.EDUC.,42, A-601-2 (1965). The Macalaster Soientific Corp., 186 Third Ave., Waltham, Mass. 02154, sells a complete set of these 100 chemicals in a ease convenient for classroom use; also TOPS devices and projectors. a This 1967 UNICELL is simpler than the model published in the J. CHEM.EDUC.,43, A 747 (1966). ' J. CHEM.EDUC.,42, A 409 (1965); (b) A 461 (1965); (c) 43, A 349 (1966); (d) Reference in footnote 1. 6 References (a)-(c) in footnote 4. 6 Daylight projector, quarts-iodine lamp, $35, J. CHEM.EDUC.. 42, A551 (1965); student dark-room projector, 110-220 v ao floodlight, 515, ibid., 40, A523 (1963); lensless projector, $0.50, ibid., 43, A747 (1966). S e e footnote 1. See footnote 6. A 12-v cluhrt-iodine automobile headlight can aho he used. Spray with heat-resistant paint, leaving a-clear window about 4 X 10 mm. lMount with Lamp horizontal, projects (as in Fig. 3) on a wall about 1 m sq. A picture-hook of 200 TOPS experiments, as shown in this article for nine picture-hook experimentswill be available by the Fall of 1967. For information write the author of this article, who will reply when the picture-book is available. We are indebted to the National Science Foundation for supporting a project under which most of this TOPS material was developed.
1. 3. 4. 5. 6. 7. 8. 11. 12. 13. 15. 17. 22. 25. 26.
CHGOOH (vinegar) AlCh (aq) NHIOH ShCL (aq) AsCL (aq) CsHs Bromcresol green (aq) C ~ O H ) (I a d (limewater) CCld (avoid contact) C1. (aq) CuCh (aq) CzHsOH 6 M HCI Kerosene oil Ph(CHaCOOh (aa)
28. 30. 33. 35. 36. 37. 39. 40. 41. 43. 44. 46. 47. 49.
Hg Methylene blue ( a d NiCL (aq) Phenolphthalein in CIHEOH KBr (aq) K1Cn07 (aq) KI ( q ) ~~d dye (aq) AgNOs (aq) NaCl (aq) NaOH (aq) N a 8 (aq) Starch (aq) (1%) 6 M HISOl
Solids
51. 52. 53. 56. 57. 59. 60. 62. 63. 64. 65. 66. 67. 68. 71. 72.
Agar (gelatin) Alka-Seltzer A1 wire (thin) NH~NOI BaClz.2Hz0 Borax, NanB40r10H30 CaO (fresh) Carbon (cigarette filter) CoCl2.6HlO Cu mire ( t h ~ n ) ~ e t e r g e n (eo'ap) t FeCls.6Hn0 FeS01.7H90 Glass wool (or cotton) Fe strip ' Pb foil
73. CaCOa, limestane 74. Mp ribbon
92. 93. 94. 95. 96. 99.
NanS0~ Nan&Oi, 5HaO Steelwool Sucrose. C I A & Sulfur, flowers Zn, granular ~~
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Volume 44, Number 6, June 1967
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TOPS UNI
Plating E - 1
Fig. 1.
TOPS UNICELL, 1967 Model with accenorie%
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CELL
Tested Overhead Proiection Series
THE UNICELL The single device, named the UNICELL,$ shown in Figure 1, is ample for the teacher when he first adopts the TOPS technique; later be can "graduate" to a more sophisticated 12-device kit described in the TOP ~ e r i e s . ~ Making the Device
The device ismadefrom Plexiglas plastic (polymethylmethacrylate) ; glass and wood covered with chemically resistant epoxy lacquer can be substituted but is not as satisfactory. If 0.5-cm. or '/An. stock is unavailable, cement two 0.25-cm. or '/=in. sheets together. (1) Parts required are four dividers 8 X 1.4 X 0.5 cm, one base 12.5 X 3.3 X 0.5 cm, and two clear sides 12.5 X 8.7 X 0.25 cm. I n the top of each divider, bore a hole 1.5 cm deep and thread (the author used a '164 in. drill and a 8/32 tap). (2) Cement the four dividers to one plastic side, using the base as a spacer. This is done by holding two pieces firmly together for the count of 100 after running a tiny drop of cement into their juncture from a dropper with a fine point. The cement is made by dissolving 1-5 g of plexiglas in 100 ml of ethane, 1,1,2-trichloroethane, chloroform, or other solvent to give a water-thin solution. The solid end of each divider should be flush with the bottom of the clear piece; the threaded ends will be about 0.7 cm short of the top of the clear side. If any cement smears on the clear side, wipe off at once with tissue paper or cotton. (3) After the four dividers me cemented in place, rub them across a piece of fine sandpaper lying flat on the table to m&e the surface plane. (4) Cement the second clear side in place. (5) Rub the bottom of the assembled piece on sandpaper to make it flat. (6) Cement the base in place. (7) Run more cement into all joints, tilting the cell so the cement runs into all cracks to assure tightness. (8) Finally, dry for a t least an hour before pouring water into the cells to test for leaks. UNICELL Accessories
The UNICELL accessories are shown in Figure 1 also. Their dimensions are not critical, and can be judged from the drawings surrounding the UNICELL which show their applications. The designations G-1, H-3, etc., are from the original TOPS a~ticles.~ Details of accessories follow.
(1) A 60-ml wide-mouth bottle with 2-bole stopper, delivery tube with rubber connector and dropper. (2) A 1-hole No. 00 rubber stopper. (3) A cork-stoppered 12- X 100-mm plastic gas holder. (4, 5) 0.5-cm od copper tubing for gas delivery and distillation. (6, 7) 12- X 100-mm glass test tubes and rubber O-rings, or sections cut from rubber tubing. Liquids in these tubes will project well only if the tubes are immersed in water in the UNICELL. (8) 13- X 3- X 0.4cm. asbestos stage. (9) Transparent scale. (10) Coca-Cola cap. (11) Two electrodes consisting of 10 cm of 0.02-cm platinum wire passing through a cork to make contact with a thumb tack; 10- X 75-mm plastic or glass tubing. (12) Glass thermometer with rubber tubing well. To fill, warm the bulb in the hand, baK-fill the well with 50: 50 ethyl alchol: red dye (aq). Upon cooling, the liquid descends; remove bubbles by gently blowing the fluid into the bulb, then allowing the fluid to return to the capillary. To remove fluid, warm the bulb, then so& up excess fluid from the well using filter paper. (13) U-tube with cork. This is for pressure measurements, as shown in next section. (14) Alcohol burner. This can be made from a small glass bottle, notched 1-hole cork, and wick. (15) Two to twenty-milliliter hypodermic syringe with No. 24 needle. (16) Aluminum plate, 14.8 X 1.8 X 0.1 cm, with three 15-mm holes, 4, 8, and 12 mm from the end; one 3-mm hole 10 cm from the left end; and two slits, 4 X 4 mm, at each end. The latter accommodate: (17) A set screw (the author used a 6/a2 machine screw 2 cm long, with a metal tube 1cm long crimped on it as shown in Figure 1). The following simpli6ed substitutes can be made. For item 12: fill a glass vial, 4 cm long X 12 mm od, onefifth full of red manometer liquid. Insert a glass tubing 15 cm long X 2 mm id passing through a 1-hole No. 00 rubber stopper. This serves as a simple thermometer. Use a similarprocedure for item 13, but fill the vial one-quarter full of clean mercury. To measure the vapor pressure of a liquid, e.g., acetone, put a few drops on top of the mercury in the vial (or insert a strip of acetone-moistened filter paper). Immerse the vial in the UNICELL chambers at two different temperatures. For item 16: No. 16 copper wire, or a pipe cleaner wire can be twisted to form a holder for the test tube suspended over the burner; screw 17 passes through a smaller loop. For suspending the two electrolysis tubes a pipe cleaner can be twisted into a double loop, with ends resting on the two middle dividers. Volume 44, Number 6, June 1967
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H-3 H e a t rack
MP Measuring pressure
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Tested Overhead Projection Series
STUDENT WORKBOOK Questions
Demonstrations, properly conducted, involve active student participation just as much as any class "experiment" or "experience." The TOPS UNICELL m&es it possible for each student, individually, to carry out the experiment on the writing arm of his lecture-room desk. The teacher projects it to confirm student observations. The reaction between Fe and Cu2+is given here as an example. I n the old, conventional, macro-demonstration the lecturer lifted an iron bar from blue cupric solution to demonstrate that the iron had been coated with red Cu. Contrast this with the corresponding UNICELL demonstration; note the research experience in which the student is involved below. The experiment is the first one in the Picture-Book Experiments shown on the two preceding pages. The student must answer questions relating to the following diagram, Figure 2. Observations
1-14. Colors? 15. Temperature in cells? 16. Physical changes? Explanations
17. Colors? 18. Chemical equation, including flow of electrons? 19. Whv is 6.7 aeen? 20. do' tce steelwool fibers suddenly and explosively crumble? 21. Why does some of the yellow solution stream up-
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Figure 2.
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Reaction of C u Z * with Fe
Journal of Chemical Education
wards (toward 5) whereas other of the yellow solution streams downwards (toward 12)? Research
22. Suggest researches, preferably with results amenable to graphing, suggested by your observations. You w ill be sent to the laboratory, in groups of five, to carry these researches out. Homework
Consult tables of electromotive force, atomic weights (round off to three digits), and heats of reaction. 23. List ten cations, with their half-cell potentials in descending order of chemical activity. 24. What voltages would cells, made of the following pairs of metals, give: Cu-Zn, Mg-Ag, A1-Cu? 25. Name three metals which would behave like steelwool in dis~lacingCu2+. Three of which would not. 26. Assume that the middle chamber of the UNICELL contained 10 ml of solution with 1.7 g of CuC12.2H20,that 1 g of steelwool was used, and that the temperature rose 12°C. How many moles of Cu2+and of Fe were present at the start of the reaction? At the end, assuming Cu Fez+ formed (the Fez+ later oxidied to Fea+ in solution)? What weights of Cu or Fe remained? 27. What was the heat of reaction per mole of Cu2+? Contrast this with the accepted published values. Account for any difference in the two values.
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Tested Overhead Projection Series
TEACHER'S MANUAL
Answers General lnstrudions to the Teacher
Notice that there are three phases: 1. The Experiment. Carried out by each student in his own UNICELL. Then, in teams of five, using a lensless projector (see next page). Finally, by the teacher who projects his UNICELL to a 2 X 2 m size on the side wall whiie the student records observations and explanations. 2. Research. Suggested, planned, and carried out by the students in teams of five each, working au hour in the laboratory. Teams return to report their findings to the class. 3. Homework. A report of his research, and answers to homework questions involving reference work and mathematical calculations. Special lnsfrudions for the Fe
+ Cuz+Experiment
1. Use CuClz (aq) diluted to blue, not green. Use coarse (Grade No. 1) steelwool, loosely rolled. 2. After reaction has occurred, exhibit the UNICELL: the red Cu is visible. Have a student feel it (center chamber is warmer). Use the thermometer to find the temperatures of the cell chambers; have the class record the results. 3. Rinse the cell out at once or the plastic will soil. Student Workbook:
Answers to Questions
The student may give the following answers. 1. Blue, CuZ+. 2. Blue, Cue+. 3. Grey, Fe solid. 4. Blue, Cue+. 5. Yellow, Fe3+. 6. Green, blue CuZ+ yellow Fea+. 7. Ditto. 8. Yellow, Fe8+. 9. Red, Cu solid. 10. Grey, Fe solid. 11. Blue, Cu". 12. Yellow, Fe8+. 13. Yellow, Fea+. 14. Red, Cu solid. 15. Middle cell temperature rose 12'C. 16. Fibers tore loose. almost exwlosivelv. from the ball of steelwooi. Yellow hution; streamed upwards and downwards from the ball of steelwool. A layer of yellow solution formed on top. The ball of metal finally collapsed and sunk to the bottom of the chamber, as red mud (Cu-coated Fe).
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Explanations
17. 18. 19. 20.
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See 1-14 above. Fe Cue+ Cu Fee+which oxidized to Fe3+. Blue Cue+ yellow Few gave a green solution. Heat of reaction and resulting convection currents ejected the crumbling fibers. 21. Fea+solution, hot from heat of reaction, was less dense than the original Cue+ solution and streamed upwards. On the underside of the steelwool the iron absorbed the heat, and the colder, more dense, Fea+ solution streamed downwards.
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Research
22. Researches suggested by, and subsequently carried out by, the students might be the following. (a) Place yellow Fe3+in the outer compartments. Graph reaction of steelwool with varying Cue+ concentrations versus time for the middle compartment to reach this yellow color. (b) Same as above, with varying grades of fineness of steelwool. (.c.) Same as above with H + or other ions added to the solution. (d) Same as above with the initial temperatures of the Cue+a t 0.25. and 60°C. (e) Contrast Al, M ~ , and ' Fe reacting with Cu2+. (f) Measure, using the UNICELL Mo accessory, the heat of reaction under varying factors mentioned above. Homework Answers
K, 2.92; Na, 2.71; Mg, 2.34; Al, 1.67; Zn,0.76; H, 0; Cu, -0.34; Ag, -0.80; Pt, -1.2; Au, -1.68. Cu-Zn gives 1.1volts; Mg-Ag, 3.41 volts; A1-Cu, 2.01 volts. Mg, Zn, and A1 would displace Cu2+; Ag, Au, and Pt would not. Moles of Cu2+ = 1.7/170 = 0.01. Moles of F e = 1.0/55.9 = 0.018. The Fe was in excess. Moles of Fe remaining = 0.018 X 55/8 = 0.045 g. Heat of reaction per mole of Cu2+ is 10 ml X 12"C/0.01 = 12,000 calories. Literature value is 18,000 calories. These two values diier because much heat was lost by radiation, the weight of Fe or concentration of CuZ+solution diiers from that of water, the Fe was heated up but was not accounted for in the calculation, etc. Volume 44, Number 6, June 1967
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PROJECTORS Commercial Models: The more expensive overhead projectors suitable for chemical experiments cost $150400 and usually have a brilliant "daylight" quartziodine 110-v ac lamp costing about $8 and lasting about 80 hr. The less expensive models cost about $100, use a one dollar, 150-w, 110-200 v ac floodlight with 2000-hr lifetime; they must be operated in a nearly darkened room and are recommended only for students or for teachers with a limited budget. Suppliers include the Laboratory Furniture Co., Old Country Road, Mineola, N. Y.; the Macalaster Scientific Corp., 186 Third Ave.; Waltham, Mass., the Central Scientific Co. (CENCO) 1700 Irving Park Road, Chicago, Ill.; the Thermofax division of the Minnesota Mining and Manufacturing Co. (3 M), St. Paul, Minn., and branch offices; the Edrnund Scientific Co., Barrington, N. J. 08007; the Charles Beseler Co., East Orange, N. J.; Hugh Wood, Ltd. (Ealing) 23 Lehman Street, London E-1, England; the Technifax Corp., Holyoke, Mass.; and others. Homemade Projectors.6 Both the daylight quartziodine projector and the 150-w spotlight projector shown
in Figure 3 can be built in a few hours for about $35 and $15, respectively. Lenses, lamp, and reflector are available from the Edmuud Scientific Co., Barrington, N. J. 08007, and the ventilating fan, a Skipper Venturi SKR can be purchased from Radio-Electric, 7th and Arch Streets, Philadelphia, Pa. Full details are given in the TOPS reprint7and TOPS article^.^ A Lensless Projector. A satisfactory, inexpensive (half a dollar!) projector is shown in Figure 3. It is simply a single-filament automobile bulb (No. TS 1133 or TS 1183) to which two wires are soldered, leading to a 6-v source (a 6-v dc automobile battery, or battery charger output, or 6-v ac from a transformer plugged into 110 or 220 v ac). The bulb is sprayed with heah resistant lacquer leaving a clear area 10 mm in diameter in the center of the bulb. A rubber tubing is slipped over the base, which fits into a slot as shown in Figure 3. The plywood base is 40 X 15 X 0.5 cm; the stage is 15 X 4 X 2 cm and is 14 cm from the screen. The slotted bulb-support is 15 X 2 X 2.5 cm. A translucent paper screen is placed 40 cm from the bulb, and the reaction vessel interposed. Reactions can be seen in color on the screen even in a large auditorium, and depth of focus is several times that of conventional project~rs.~
Figure 3. Three homemade projector,. Top: A quartz-iodine lamp is employed in this daylight projector; cost to moke, $35.00. OAS *1.1 ,--,.
I b conrtruction war described in this Journol, 41, A551
Center: A student pmjeetor for o dark room is mode with a 150-w rpotlight or a light source, cost $15.00. Journol, 40, A523 11963). Bonom; A lensless projector using o 6-v ovtomobile lamp a* a w m e , cost, $0.50.
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Its construction was dexribad in this
