overheod projector demon/trotion/
edited by DORISKOL8 Bradley University Peoria, IL 61625
Hubert N. Alyea Frick Chemical Laboratory, F'rlnceton, NJ The exciting revival of interest in the overhead projection of chemical ex~erimentahas inspired the author u)develop an entirely ned and very simple projection technique usinga standard-type overhead projector. Ordinary horizontalstage projection cannot show reactions in test tubes or the rise of bubbles during the generation of gases. Vertical-stage projection, on the other hand, is cumbersome and expensive; the two lenses for the TOPS Projector-adaptor,' which originally cost $7, now cost about $50. This new projection technique uses a simple support device inclined at an angle of about 20". When placed on the horizontal stage of an ordinary overhead projector, it is able to tilt the object being viewed so that the perspective is changed and the projection stimulates that of a verticalstage projector. Test tubes, bottles, electrolytic cells, gas generators, and other objects can he viewed in vertical profile, and bubbles can be seen rising during chemical reactions. The Tllted Stage Base. Cut a 5- X 4'h-in. hole in the center of a 12- X 12- X in. plywood board. Deck supports. Cut two right-angle triangles 5 in. long and 2 in. high out of %in. plywood. Deck. Cut a hole in a 5'h- X 4- X %-in. opaque (white or black) acrylic sheet to form a frame with sides and bottom 3/8 in. wide and a top 3/, in. wide (or cut strips and cement them together to form the frame). Assemble these pieces as shown in Figure 1.Use nails and glue for the plywood; the bottoms of the triangles should he flush with the underside of the base. Use Duco Cement for the plastic deck. If you prefer to have a transparent space on the horizontal stage on which to write equations (for projection) here are alternatives: Method l Replace the wooden stage with a 5%- X 4-in. acrylic plastic stage that resembles the center portion of Figure 1. Make this as follows. (1) Use a 5%- X 4- X 'I8-in. slanting deck cemented to two right triangles of plastic 5 in. long X 2 in. high. (2) Brace the junctions of deck and triangles with 5%X Y4- X jig-in. acrylic rods. (3) Cement a 4- X '14- X %in.
'TOPS hojector-adaptor, see J. Chem. Educ. 1978, 55, 788:
-. Readers who find mese lnshuctlons too sketchy should consult
.- . - .
1979 -, 56~7 -5 .1. ~
Flinn Scientlflc. Inc.. 131 Flinn Sbeet. Batavia. IL 60510. who market TOPS items.
Figure 1. The TlHed-TOPS stage. acrylic rod flush with the bottom edge of the deck to support the reaction cells. Method 2 (1) Cut a strip 12- X 3- X %-in. off the end of the wooden stage (Fig. 1) nearest the bottom of the inclined deck. (2) Bore three %-in. holes 3 in. apart and in. in from one edge of a 12- X 3- X 1I4-in.acrylic sheet. Wood-screw this onto the stage over the spot previously occupied by the 12- X 3- X %in. piece you just sawed off. (3) Using a 12- X 1%-in.strip of adhesive tape as a hinge, fasten a 12- X 3-in. sheet of cardboard or thin opaque plastic to cover the clear plastic. Tllted-TOPS Devlces New TOPS devices, carefully designed for use on the inclined stage, are shown in Figure 2. For quality projection they must be made precisely as directed below. Each device is coded so that you can insert this new information if you already have a TOPS file. Discard your older TOPS d e ~ i c e s . ~
.Incllned Stage Accessory /stage A 41h- X 4- X '18-in. transparent plastic sheet for supporting various objects heing projected.
Btl- 1 Square, clear glass, 50-mL bottle with 35-mm cap. Rgieet on I-Stage (see above, not shown in Fig. 2). Over a burning match, hold a 2- x 1-in. piece of haeon. When it drips, drop it into Volume 66 Number 9
September 1989
765
Btl
C- 1
C-tt
4
Figure 2. TiltedTWS devices.
786
Journal of Chemical Education
Gg-Hot
Btl-1 full of brown bromine gas. See. The gas becomes colorless as hramineaddsonto the double bonds that formed when the bacon fat was cracked.
Btl-2 Tandem glass bottles. Project on I-Stage (see above, not shown in Fig. 2). Blow into bottle 1, half full of 6 M HCI. Breath carries HCI vapor into bottle 2 half full of 10%sodium thiosulfate(sq). See: opaque, white (show macro) sulfur-sol forms. Readlon Cells
Cells G 1, G2, C-3, and C-4 All cells have 4%- X 4- X %-in. acrylic backs, 4- x 4- x i/s-in. fronts, and mid-strips Y4 in. thick.
E-2 Dual Conductivity Cell. Fits into C-2. Like E-I, hut with two pairs of Cu wires leading t o asingle pair of machine screw terminals. Instead of the croas piece, cut out the plastic plate (see Fig. 2) so the wires do not touch it. Project. (1) Lower E-2 into C-2 containing commercial vinegar in one cell and 0.8 M HCL in tbe other. Press a 9(5% acid 0.8 M Ht) V transistor battery to the common terminals. See: many buhbles from the HCl (nearly 1W% ionized), few bubbles from the vinegar (less than 5% ionized). Similarly test (2) sugadaq) versus NaCKaq), and (3) 1M HCI versus 0.1 M HC1. E-HZ0 Electrolysis of water. Fits in C-tt. Seal two Pt wires in a 3- X 3- X %-in. acrylic double box mounted on a 5- X 3%-in. acrylic backing. Bore a3/&n. hole in the bottom of each box. Project. Using a 12-V toy train transformer electrolyze 0.5 M HzSOI. Reverse current when one cell is two-thirds full of hydrogen. When both cells are full of 2H20 02, stopper each hole with a cork. Now explode the gases with a lighted match.
+
Project. Ten drops of vinegar in water plus drops of phenolphthalein. Stirring with a stick, titrate with 0.5 M NaOH. Calculate the molaritv of the acid to confirm its leealitv (usuallv labelled as 5% acetic &id, which is 0.83 M CHJCOO~~).
G2 CuCb(aq) in cell 1. CuClz plus a loose ball of steel wool in cell 2. See: colored streamera due to displacement and heat of reaction. Exhibit red Cu (macro). FeCMaq) in cell 1m show yellow femc ion. NHIOH + FeCldaq) in cell 2 toshow (macro) orange Fe(OHl3 ppt. Transparent deep red colloidal (Fe(OH)d, in cell 3 from boiling FeCldaql (macro). Fill all cells with water plus dmps of phenolphthalein and bromcresolgreen indicators (pH 7, blue).Tocelll add dropsof HCl (pH 2 vellow~.Tocells2.3.and4add5dro~sof0.5MKaOH (nH 12.nolct &om red nbenolnhthalein nlus blue bromcreso~meen).~ack-titrate p H 4 in cell 2 with "in& to give blue 7 in cell 3, and
P'H
C-glass For reactions using organic solvents that attack plastic cells. Acrylic strips % in. thick, sandwiched between 5- X %in. singleweight glass plates. Cover the sharp edges with adheaive tape. Project two C-glass cells containing (1) KBr(aq) and (2) KI(aq). Stir in drops of fresh hypochlorite (aq). Then add cnrbon tetrachloride (danger!Wash it off your skin). See: both Br(aq) and I(aq) are brown, but in CClr hromine is brown, and iodine is a beautifulviolet.
G a s Generators
GIand62 Bend three 7-in. lengths of soft copper refrigerant t u b i i 'Is-in. o.d., as shown in Figure 2, to clip snugly over the sides of C-1, and C2. Fit into 12- X 75-mm test tubes. Projection in G-I. In the test tube put 2 mL of 0.2 M HCl plus 0.5 g NaHS03. Lead into C-l containing (a) yellow KzCrzO~(aq)plus drops of HCI or (b) pale purple KMnO,(aq). See: SO2 bubbles give green Cr3+ or colorless MnZt. Projection in G-2. Place 1ggranualar Zn in each test tuhe. Dump 1mL of 0.2 M HCI into one test tube and 1mL of 1M HCI into the other. See: five times mare bubbles of hydrogen from cell 2. Bend, in three dimensions, a 14-in. length of copper refrigerant tubing, 'IS-in. o.d., (see Fig. 2) so that i t can support a 12- X 75-mm test tube in the flame of a homemade alcohol burner l-in. hieb. Project. KNaq) in C-1. In the test tube heat 2 mL cone. HCI plus a pinch of MnOl. Then add a drop of starchmq) ur C-1. See: chlorine gas bubbles inm the Kl(aq), liberating brown I(aq). Starch gives
-
G-n Bend a 7411. length of Cu refrigerant tubing as shown in Figure 2. Put a pinch of MnOz plus 2 mL 3% hydrogen peroxide in a 12- X 75mm test tube, and insert it and the delivery tuhe into water in C-tt. Lower the mtoppered gas holder over the delivery tubing. Now stopper it. Collect the off-gas and test for oxygen with a glowing splint.
Gff Test-tube cell. A 7- X 4- X '1s-in. clear acrylic back, a 4%- X 4- X Ya-in. front. and an omaue back niece. 3- X 3- X %c-in. A hase 4- X lli- X $-in.'thick. T d o i d e s 7. x' '1,- x '%-in. thicc Cell C-tt holds four 13- x 100-mm test tubes suspended on !r.in.-dia. rubber Orings. Optional. in the test tubes insen rubber stoppers bearing 'ISin. plastic capillary tubing 3 in. long. Project. See T-6. Display vanadium samples in test tubes in C-tt.
Electrolytic Cells E- 1 Fits in C-1. Anchor two No. 26 copper wires through holes a t one end of a 5- X 3- X %a-in. acrylic plate. At the other end attach them to a pair of machine-screw terminals. The two wires are passed over a 3- X V4- X %s-in.-thick cross piece t o keep them away from the plate, othenvise any generated gas bubbles may stick to the plate. Electroplating. Immerse E-l in CuCldaq) in C-1. (1) Press a 9-V transistor battery to the terminals. See: the cathode thickens as Cu plates out. (2) Reverse the current by rotating the battery 180'. See: the Cu plate falls off; the other wire thickens. Electrolysis. Electrolyze KI(aq) plus drops of phenolphthalein. See: brown iodine around the anode, hydrogen bubbles and red phenolphthalein (from OH-) amund the cathode.
Useful for generating and storina many gases. Ccmnect a 12- X 75mm test tube via copper and plastic tubing m s 10-mL plastic syringe. Project. Put 0.5 g FeS plus 1mL of 1M HCL in the test tube. Have the syringe, plunger all the way in, lying on the horizontal projector stage. See: plunger moves as the syringe fibwith HzS gas. Macro. Attach a drinking straw to the syringe, and inject a few bubbles of HnS into four aqueous solutions containing Zn2+,Cu2+, Sb5+,and AsS+ions. See: precipitation of white ZnS, black CuS, orange Sb& and yellow A82S5. Relate to qualitative analysis procedures. Thermometer
Them A thermometer. Fits into C-tt. Seal a 'IS-in.-0.d. plastic capillary tuhing 6-in. long into a 3- X 1%- X 31s-in. acrylic box. Preparatory adjustment. Immerse the entire box in hot water for 2 min. Now invert, holding the capillary tubing immersed in water colored with red fwd coloring, until a pool 5 mm deep has been drawninto the cell. Holding the 1%-in.side vertical, gently blow any liquid out of the capillary into the cell box. Now, turn the cell upright; the meniscus will be near the bottom of the capillary. Raise the liquid to any desired height in the capillary by gently blowing in a few tiny hubbles. Volume 66
Number 9
September 1989
767
Calibration. Measure the positionof the meniscus when the boxis completely immersed in water at two temperatures 20 'C apart (it will be about half the box height). Project. (1) Use the T h e m box completely immersed in water in C-tt to stir in (a) 5 g of unslaked lime (exothermic) and (b) 5 g of photographers' hypo, Na&0r5Hz0 (endothermic). (2) Mix 20 mL of 1M NaOH plus 20 mL of 1M HCl. Calculate the heat of neutralization in calories per mole of NaCl formed.
Trays
T- 1 Cement a thin plastic ring 3 in. in dia. X 1in. high to a7- X 3- X %in. acrylic sheet. Project. Danger! Before dropping in scdium or potassium, cover T-l with a ~ratective6- X 4- X %-in. plastic sheet on the inclined deck, since ixplosionusually occurs, es&cidy at the very end of the reactions. Handle the Na and K only with tweezers. Danger! Do not use a piece of Na or K larger than a match head. See: Potassium skips around on the surface of the water more vigorously than .din",
Notes. (1) A bit ofdetergent in the water will prevent the piecesol Na or K imm sticking to the ring. (2) A drop of phenolphthelin will trace a red path wherever alkali forms.
788
Journal of Chemical Education
T-2 Cement two rings %in. in dia. X %-in. high to a 7- X 3- X 31s-in. acrylic sheet Project. (1) Add a few tiny flakes of camphor t o each cell half full of water. (Do not touch the camphor; the oil from your fingers changes the surface tension.) (2) Now add a drop of detergent(aq) to one. See: (1) m a t e due to ineoualities . . The camohor bits whirl and -. in surface tension. (2; Surface tensions change, pushing the eampbor to the walls of the cell. T-6 Cement six 1-x 1- x %-in. plastic hoxesto a 7- X 3- X 'IS-in. acrylic sheet. Macro. Completely dissolve 2 g ammonium vanadate in 50 mL of 6 M HzS04. Add 5 g of granular zinc. Project. As the solution changes color, put samples in five of the boxes. They will be (1) yellow ammonium vanadate, NH4VO3, (2) green (?), (3) blue vanadyl sulfate, V(S032, (4) green vanadic sulfate, V2(SO& and, after 15 min of reaction, (5) a beautiful purple vanadous sulfate. V(SOn).Alternate: ~roiectthe solutions in test tubes in C-tt ~ & yo& e students e=plin why (2) was green (a physicalmixture of a + c) and, given the formulas, calculate the four valences of vanadium.
