Tested Overhead Projection Series Cornp~ledby
HUBERT N. ALYEA Princeton Universitv
9. ATOMIC STRUCTURE. RADIOACTIVITY (continued)
C. Planetary Dem. 395-Covalent
Bonds, Cu(NH3),++
To show: Formation of the complex Cu(NH&++ as an example of coordiriate covalcnt binding. Materials: NHraq, C-3, stirrer, CuC12-aq. Procedure: (a) Project C-3 with cach cell two-thirds full of CuCl,aq diluted to pale but distinct blue. (b) Add NHraq dropwise with stirring to Cell 2 until permanent precipitate forms. (c) Add NHa-aq dropwise, with stirring, to tube 3 until the precipitate which first forms, redissolves. Observations: (a) Pale blue hydrated Cu++. (b) Pale blue (show macro) Cu(OH)%which projects a dirty green. (c) Deep purple cupric tetra-ammine ion, Cu(NH&++. In this, the N of cach NH3 furnishes two electrons to the cupric ion to give coordinate covalent binding. Dem. 396-Hydrogen
To show:
Bonding
Hydrogen bonding as evidenced by viscosity.
Procedure: Nearly fill three round plastic boxes, 3-in. dia. X 1-in. high, with glycerine, water, and ethanol: on each liquid float a match-stick. Place the boxes on top of one another on the horizontal stage and project. Momentarily swirl them simultaneously. Observation: Hydrogen bonding, evidenced by high viscosity is greatest in glycerine, least in ethanol; the match ceases swirling sooner in the most viscous. Reference: (1957).
CAMPBELL, J. A., J . Chem. Educ. 34, A105
10. GROUP ZERO.
THE ATMOSPHERE
+
30 ml H,O. Materials: Soh. A . 30 g NaOH Soh. B. 3 g pyrogallol 10 ml HzO. Mix equal volumes of A B just before using. A 20-ml hypodermic syringe.
+
+
Procedure: (CARE: alkaline pyrogallol solutions is extremely caustic and also stains the skin.) Avoid warming syringe with hands. Fill syringe with 20 ml air. Project t o show volume of gas. Now draw in about 2 ml alkaline pyrogallol solution. Stoppering nipple end, shake solution for two full minutes. RTow push plunger t o just eject all liquid, hut leaving all gas in the syringe. Project and read new volume. Observation: I n two runs 10 ml of air reduced to 8.3 and 8.8 ml correspond to 17 and 12% respect,ively. Dem. 398-Paper
Burned in Air
To show: A fallacious belief in what occurs when paper is burned in air in a glass inverted over water. Materials: of paper.
H-3 plastic tray, M-p square box, pieces
Procedure: Fill the box full of water, and pour it into the plastic tray on the projector. Set fire to a small crumpled piece of paper, hold it for a few seconds at the mouth of the inverted box, then quickly lower the box and burning paper into the water. Observation: The water rises
the way up. Why?
Discussion: Refer the class to Dem. 22 where steelwool rusted, and Dem. 23 where P burned; in these cases the water rose also '/a because the 21% oxygen in the air was consumed, creating a vacuum. But with burning paper the water should not have risen because (a) there is no volume change when 1 volume of O2 is replaced by 1 volume of COz and (b) paper does not burn in under 16% oxygen in the air, so only a quarter of the oxygen was consumed. Answer: (a) the water rose up because heat expanded the air in the box and, upon cooling the gas it contracted; (b) it could not rise more than because that is the volume of water poured into the tray.
A. Atmospheric Pressure 2. CARBON DIOXIDE IN THE AIR
See Dems. 7 89, 190.
B. Substances in the Air Dem. 397-Air
+ Pyrogallol
Experiment developed by W. H. Slabaugh. Analysis of a gas, such as air, for oxygen
+ Limewafer
Experiment developed by Evangeline B. Klug, To show:
1. OXYGEN
To show: content.
Dem. 3 9 e A i r
COzof the air can be trapped by limewater.
Materials: Clear, saturated limewater; C-2, adhesive tape, microscope slide. Procedure: Three-quarters fill G 2 with limewater. Tape a microscope slide over cell 1 t o shut out the air. After two hours, project. Stir cell 2. Volume 44, Number 7, July 7967
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