Tested Overhead Projection Series Complied by HUBERT N. ALYEA Princeton University
15. BORON AND SILICON
B. Silicon
A. Boron
1. SILICON DIOXIDE Dem. 466-Absorption
Dem. 464ÑBori Acid from Borax
To show:
To show:
The formation of boric acid from horax.
Reaction: 4HaBO;.
Na2B407
+ 2HC1 +
5H.O
-+
2NaCl
+
Materials: Methyl orange indicator, conc. HCl, borax (Na2B407-10H20),funnel and filter paper, stirring rod, H-3. Procedure: (a) In H3 project a culture tube containing 2.5 g borax 20 ml HsO; boil and stir t o dissolve. Now add 2 drops methyl orange indicator conc. HC1 dropwise until the indicator turns pink. Let cool. (6) Place funnel with filter paper on culture tube 2, pour the colored solution through the filter, and discard filtrate. Now pour hot water through the crystal in the funnel. Let cool.
+
+
Observations: Upon cooling the solution, bone acid crystallizes out. The colored solution can be filtered, and the white crystals of pure H3B03recovered. Exhibit them macro. Note : Solubility of HiB03 in 100 g water is 1.95 g a t O°Cand 39.1 g a t 100°C See Dem. 253.
by Silica Gel
The absorption of ether vapor by silica gel.
Materials: Mp-760 mercury-filled manometer; ether, silica gel, small vial about 1 in. high. Procedure: Fill Mp box with ether vapor by putting m 2 drops and allowing the liquid to evaporate. Connect to Hg manometer and project. Now dump 20 I of silica gel into the ether vapor, stopper tightly, and at once read the manometer. Read at 15-sec intervals Observations: The pressure drops steadily some 100 mm as the ether vapor is absorbed on the silica gel. Note: Also try NHg, 802, water vapor, etc. Dem. 467-Heat
To show: vapor. Materials:
of Absorption by Silica Gel
Heat released when silica gel absorbs water
Mo, silica gel.
Procedure: Project Mowith room temperature scale, and box filled with silica gel surrounding gas bulb. Add a dropperful of water. Observations: As the moisture is absorbed, the temperature of the gel rises about 5% Note : Also try ether vapor, NHi, SO2.
Dem. 465-Borax
Beads
Experiment developed by LeRoy G. Hornbeck. Materials: Borax (sodium perborate NaaB&. 10H20), thin P t wire on end of glass rod, H-4, alcohol burner, aqueous solutions containing ions of Sh, Co, IT, Cu, and Fe. Procedure: (a) Light the alcohol burner in H-4 and project. In the flame heat a '/r-m. loop of Pt wire; then dip it into borax, and reheat. (6) Now dip the bead into one of the solutions, and re-heat. Repeat with other solutions.
Dem. 468-Absorption
on Kaolin
Experiment developed by Charles Owens. To show: The removal of methylene blue or of brown coloring matter from sugar solution by kaolinite (A12H2(Si04)2H20).
-
Materials: Kaolin, methylerie blue-aq, brown sugar, glass wool, H-3.
Oxzdizing flame
Reducing flame
Procedure: As in previous two demonstrations. This time, however, it may be necessary to run the solution through the kaolin several times to achieve noticeable absorption.
yellow green-blue yellow-brown blue
green red to colorless gray blue
Note: An alternate procedure is to shake a tube quarter-full of kaolin with the colored solutions, and then allow to stand overnight. Contrast with tube of original solution.
Observations: (a) The horax bead is clear and colorless. (b) Different colors are obtained, viz., Fe Cu Sb Co
2. SILICATES
Volume 45, Number 2, February 1968
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A151
