Tested Overhead Projection Series Compiled by HUBERT N. ALYEA Princeton University
17C
I 9F Suggested by Paul L. Reber, John Adams High School, South Bend, Indiana (2965).
To show: Formation of oxides of nitrogen by sparking in the air.
To show: Redox reactions involving iodine, HNOJ, and S203-.
Materials: Tesla coil with wires, phenolphthalein indicator, NaOH-aq, conc. H2SOl, FeSOraq, long-stemmed funnel; a 2-02. wide mouth square glass bottle with stopper through which passes two nails bent inside the bottle so their points nearly touch.
Materials: Conc. HNO3, 0.1 N XI, 0.1 N Na2S203, droppers, stirrers, 3 square 2-on. glass bottles (or can be done in petri dishes on the horizontal stage).
Dem. 808-Redox
24. MISCELLANEOUS Dem. 805-Arc
Process
Procedure: Project the bottle filled nearly to the nails, with water containing a few drops of phenolphthalein and rendered slightly pink with a drop of NaOH-aq. Pass an arc for ten minutes. Stir in a dropperful of FeSOraq; gently (CARE) pour in a '/%-in. layer of conc. H2S04through the funnel immersed to the bottom of the bottle.
Reoclions InvoIving ladine
Procedure: (a) Project; to three bottles half-full of KI-aq add HN03 dropwise, with stirring. (b) Then to bottle 2 add thiosulfate dropwise, with stirring. (c) Finally, to bottle S add thiosulfate to colorless, then conc. HN03 dropwise. Observations: (a) All bottles release brown 12. (b) The I? decolorizes. (c) The brown Iz re-forms. Reactions are
-
6 1 - + 8 H + + 2NOa--3L+2NO+4HpO
Observations. Oxides of nitrogen form; with water they form HN03, which gives the nitrate ring test a t the juncture of the conc. HzS04and aqueous layer.
2
s101-+ la
Dem. 809-Oxidation Dem. 806-Formotion
of N O and NO2
17C
Developed by B. Berg and G. Harrison, Princeton, 1969. To show: Formation of NO and its subsequent reaction with oxygen in the air to form brown Not. Materials: NaN02, 2-02., narrow neck square bottle with neck). FeS04.7H20, (3 X 11/* X NaNOz. Procedure: Project the dry bottle containing 1 g FeS04.7Hz0 0.5 g NaN02 (amounts are critical). Add 4 drops water. (Amounts are critical.)
+
Observations: Colorless NO forms and immediately reacts with oxygen of the air in the bottle to form reddishbrown NO2. Additional NO sweeps this out of the bottle, which now appears colorless. Fresh NO, emerging from the narrow neck of the bottle encounters more air, forming a cloud of brown N02.
2 I-
+ &0.-
States of Vonudium
2 18
To show: The following. Oxidation Number
Formula V++ v+++ [VO]++ vO]+++ [VOz]+ [VOa]wO4]--[V04]-
Name vanadous vanadic vanadyl vanadyl vanadyl metavanadate orthovanadate peroxyvanadate
Color violet green blue pale yellow pale yellow colorless colorless red-brown
Materials: 3 g ammonium metavanadate in 50 m16 N HzS04; 3% H102,granular Zn, SOz-aqmade by generating SOz from Na2S03 HCI and bubbling through water; six test tubes; C-3.
+
Procedure: Project all six tubes quarterful of the vanadate solution, immersed in water in C-3.
and A. WISWANATHAN, Tube 1: Add a few granules of Zn and dilute to '/n after Reference: M. G. SURJARAMAN J. Chem. Educ., 26, 594 (1949). violet V++ forms. Tube 2: Add a few granules of Zn and dilute to after green V+++ forms. Tube 3: Dilute to 3/4 then add SO2-aqto form blue VO++. Tube 4: Dilute to half, then add SOz-aq to blue VO++, then Dem. 807-Solid Reactions 17E H202dropwise to form yellow VO+++ VOzC. Tube 5: Deueloped by Bro. Bosco, St. Davids Marist College, Dilute the original metavanadate to 3/n. Tube 6: DiJohannesburg, Republic of South Africa (1967). lute to half, add SOraq to blue VO++, then add Hz02 dropwise to form reddish-brown VOn-. Materials: PIJ(NO~)~, KI, H-3, culture tubes.
+
Procedure: Project tubes containing (a) 1 g Pb(NO&, (b) 1 g RI, (c) 1 g of each. Heat. Observations: ta) Brown NO*. (b) Nothing. (c) Violet I,. A534
/ journal of Chemical Education
Dem. 8 10-Tempering
To show: The tempering of iron.
21E
Materials: Two hairpins, burner, asbestos, forceps. (Test the hairpins before class, all do not work equally well.)
Observations: The cell containing the chewed bread does not turn nearly as blue as the other, since much of the starch in i t has been converted into sugar by the saliva.
Procedure: Heat both pins simultaneously. Allow one to cool gradually on the asbestos; plunge the other into cold water. Project; try to bend each one.
Note: I n the digestive process much of this enzyme action is delayed until the food reaches the stomach.
Observations: The slowly-cooled pin has lost its temper and bends easily; the other is hard and brittle.
Dem. 8 14--Action of Saliva an Starch
Note: Slow cooling forms large granules of cementite, Fe&, in the iron making it tough like wrought iron. Rapid cooling favors the formation of tiny dendritic crystals which give a hard, brittle iron, like cast iron. Dem. 8 1 1-Dehydrdng
CobaH-complex
2 1E
22F
T o show: Digestion of starch and enzymes. Materials: C-3, six 13 X 100 mm test tubes. Soln 1 g NaCl; A : boil 100 ml water with 3 g starch filter or centrifuge to give a clear solution. To this add '/lo its volume of saliva. S o h B : Add iodine to dilute XI-aq to give a pale yellow solution.
+
Devised by Howard Thomas, Superior, Wisconsin; screwdriver adaptation by M . Coccaro, Princeton, 1970.
Procedure: Fill the test tubes half-full of Soln B. At 1-min intervals add 10 drops of Soln A , shake; project.
T o show: Pink and blue varieties of cobalt complexes.
Observations: The blue starch-iodine grows progressively paler as the starch is digested by the enzymes in the saliva.
Materials: C-2, two screwdrivers with 6-in. shanks, burner, dry ice in acetone (or 13 X 100 mm test tube of ice-salt mixture). Dissolve CoC12.6Hi0 in EtOH to give a dark blue solution, then add drops of water to give a color between blue and pink. Procedure: Project C-2 with cells three-quarters full of the solution. Heat the shank of one screwdriver, and cool the other in dry-ice-acetone. Plunge one into cell 1, and the other into cell 2. Repeat, reversing ternperatures. Observations: The hot solution turns blue; the cold one, pink.
Dem. 8 12-Fehlings
Ted far Reducing Sugars
22E
Developed by Darwin Hunt.
Dem. 8 15-Finger-Mnting
24-Analyri.
Developed by Austin Finch and Jon Buchan, Princeton, 1970. T o show: Use of iodine to develop fingerprints from grease on the skin. Materials: Glass microscope slide, burner, small evaporating dish, iodine. Procedure: Press finger firmly against slide. Now heat a crystal of iodine in a dish, and hold the glass slide over it, finger-print down. Project. Observation: The iodine reacts with the grease left by the fingerprint, leaving a pattern which projects well.
To show: The Fehlings test applied to sugars. Materials: Culture tubes, 1% sucrose, 1% glucose, burners, H-3. S o h A : 6.9 g CuSOh.5H20in 100 rnl 35 g Rochelle Salts water. Soln B : 10 g NaOH (sodium potassium tartrate) in 100 ml water.
+
Procedure: Project culture tubes containing water to which have been added a few drops of ( a ) sucrose-aq (b) glucose-aq. Add a dropperful of S o h A and B to each. Heat. After precipitation occurs, exhibit macro. Observations: Only the glucose reduces the Fehlings solution, to give yellowish, then greenish, and finally red CuzO precipitate. Dem. 8 13-~n&er
in Saliva Acting an Bread 22F
T o show: Enzymes in the saliva changing starch into sugar. Materials: Two 1 cm cubes of bread; C-2, tincture of iodine. Procedure: Chew one cube of bread thoroughly for five minutes. Project C-2 half-full of water. Drop the bread cubes into each cell, stir well for one minute, then add two drops of tincture of iodine to each.
Dem. 8 16-Washing
Preciphies
24-Analysir
T o show: Effectiveness of differentwashing techniques during filtering operations. Materials: Cellite Filter-Aid, 1% KMnOa-aq, suction filter, three sintered-glass funnels; test tubes; C-3. Procedure: Mix three samples of 2 g Cellite with 25 ml of KMnOh-aq, and suction-filter them through the sintered glass funnels. Filter 1: Wash one with a single 30 ml portion of water, placing the last of the washing in tube 1. Filter 3: Repeat, but this time use two 15 ml portions for washing, placing some of the last washing in tube 2. Filtw 3: Repeat, but this time use three 10 ml portions, placing some of the last washing in tube 3. Observation: Repeated washing proves considerably more efficient than a single washing with a larger volume; this is revealed by differences in color. Note: Tom Short, Princeton, 1969 suggested shaking each of the pink Cellite solids from the funnels with 10 ml water to dissolve out the KMnOl, centrifuging to remove solid, and transferring the colored solutions to tubes 4, 5, 6. The differences in color are even more striking. Volume 47, Number 8, August 7970
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A535
