Tested Overhead Projection Series Compiled by
HUBERT N. ALYEA Princeton University
3. CHEMICAL REACTIONS OF WATER fconfinued) Dem. 107ÑHeo of Hydration of HiS04 E n l e n t developed by Liltas Brescza, LaRoy Hornbeck. Fred R o l f )
To show: Heat is evolved when conc. HaSOiiis mixed with water. (HzS04 Hz0 ->Â H%S04.H;0,the monohydrate forms).
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Method 1. Materials: MO,conc. H;SOd, dropper. Procedure: Project MO with box two-thirds full of water. Suddenly squirt a rnl or more of conc. Has04 into the water, taking care not to squirt it against the plastic (would damage it). Observation: There is rapid, dramatic rise in temperature. Notes: 1. "The water should be in before you add the HzS04, or else you might not feel too well; you might not even live to tell " 2. "If you're dom' what you oughter add the acid to the water; May your rest be long and placid, adding water to the acid!'
Method 2. Materials: Ether, iodine, H-3, conc. HzS04,6 nun tubing 6-in. long, cork stopper, epoxy cement. Preparation: Seal one end of the tubing. Quarter fill it with ether containing enough iodine to project clear brown. Push in the cork and fill the upper l/4-in. of the 6 m m tube with epoxy-cement. (Note: do not seal at both ends, this cementing technique is much safer and simpler.)
Procedure: To 100 ml water add a few drops of phenolphthalein plus a drop of very dilute NaOH to make the solution distinctly red. Fill the culture tubes half-full of this solution. Set one in H-1 and project, (a) Carbomc aczd. Drop a lump of dry ice into the red solution. (b) Nitric acid. To '/&h a tube of conc. HN03in the generator H-1 add a Cu wire. Bubble the off-gas into the red solution, (c) Hydrochloric acid. Ditto, with NaCl conc. HsS04. (d) Sulfurous acid. Ditto, with NaHS03 dil. H2S04. (e) Ortho-phosphoric aczd. Add a pinch of solid P20sto the red solution.
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Observations: Each solution turns colorless as the acid anhydride dissolves in the water to form an acid, viz. HzCO,, HNO, NO, HC1, HzSO,, and H,POi.
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Note: It is also instructive to start with sulfur and burn it in air. then dissolve the remaining material (enough SOaremains on the sulfur) m the phenolphthalein solution. Ditto, red phosphorus.
Dem. 109-Bosic
Anhydrides
To show: The formation of bases from basic anhydrides. Materzals: CaO, old lump of Na, phenolphthalein indicator solution, cell C-2. Procedure: Two-thirds fill the chambers of C-2 with water and add a drop of very dilute indicator to each. (a) Add a pinch of CaO to one. (b) Scrape off only the white coating on a lump of sodium, explaining to the class that it is a mixture of sodium oxide and peroxide. Be sure not to have any sodium in the scrapings. Drop into the other chamber.
Proceedzngs: Place a culture tube in H-3 and project. One-quarter fill it with conc. HzS04. Cautiously (CARE) pour an equal volume of water so it rests on the acid. Now insert the ether-iodine rod and (CARE)stir.
Observations: Both form hydroxides (Ca(0H)z and NaOH) and turn the indicator red.
Observations: The violent evolution of heat from the hydration-of the acid is sufficient to cause the ether to boil vigorously.
To show: The formation of potassium hydroxide by the electrolysis of KI-aq.
Notes: 1. This is safer than Tested Demonstration No 4-11, where an open tube is used and the boiling ether is ignited. The ame would not he visible on the projector. Lay the ether-iodine stirring rod away for reuse, it keeps m-
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h red, or ( b ) carbon disulfide with Iso (a) methanol ~ i t methyl odine can be used
B. ACIDS, BASES 1. PREPARATION OF ACIDS A N D BASES Oem. 108-Acid
Anhydrides
To show: The preparation of acids from acid anhydrides. faterials: Phenolphthalein indicator, H-1 with a raight not curved-up delivery tube, dry ice, Cu wire, nc. HNOa, NaCI, conc. HZSO4,NaHSO,, dil. HzSOi, 0 5 , five 4-in. culture tubes, dil. NaOH-aq.
Dem. 110ÑFormatio of on Hydroxide by Electrolysis
Materials: E-1 with U-tube and short P t electrodes, KI-aq. containing a drop of phenolphthalein indicator. Procedure: Fill the U-tube with the solution; insert in E-1, and insert the P t electrodes. Project. Switch on the current. After a few minutes, reverse the current. Observations: (a) Brown iodine forms a t the positive pole, and sinks in a streamer into one limb. KOH forms a t the other pole and turns the indicator red. (b) Reversing the current reverses the effect. Dem. I11 -Electrolytic Writing ( E x p e w " ~ " t dmdnped by Edrn" H Cooper)
To show: Formation of a base during electrolysis. Materials: 5 X 5-in. A1 foil, 5 X 5-in. blotter or heavy filter paper, 5 X 5-in. glass plate; KI, gelatin, soluble starch, ethyl alcohol, phenolphthalein, 45-v source (e.g., Burgess 230 Nx 45 v), 6 mm tubing, No. 18 Cu wire, insulated Cu bell wire. Volume 40, Number 12, December 1963
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