omMum TOPS
Tested Overhead Proiection Series Compiled by HUBERT N. ALYEA
Princeton University
Materials: Powdered iodine, 20-mesh zinc, hIo, 18 X 150 mm test tube, stirrer, medicine dropper.
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B. Heat Energy 2. PRODUCTION OF HEAT (Continued) Dem. 338-Heat
of Crydollisolion:Sodium Acetate
Experiment develqed by Euangeline B. Klug. T o show: Heat of crystallization from a supersaturated solution of CH3COONa. Materials: H-3, M0 set to read room temperature, 18 X 150 m m test tube, burner, clamp, 15 X 80 mm test tube, sodium acetate (CH3COONa3Hz0). Procedure: Half-fill the larger test tube with sodium acetate crystals, add 2 ml water and heat (macro) to dissolve. ( a ) Seeding. Project H-3. Pour part of this solution into a culture tube, place in H-3 and project. When cool, drop in a single crystal of sodium acetate. (b) Heat of solution. Project Mo. Replace the M" box with the smaller test tube, pour the remainder of the hot solution into it, allow it to stand. When cool, seed it also. Observations: (a) Seeding causes rapid crystal growth. (b) A rise of several degrees is observed, the crystallization process being exothermic. Dem. 3 3 e H e . t
of Crystallization (Na&03.5H20)
Experiment developed by G. Hornbeck and others. T o show: Heat evolved during crystallization from supersaturated NaSzO3.5H10. Materials: Device Mo, Na?SZO3.5HIO,a 12 X 50 mm test tube, burner and clamp. Procedure: Half-fill the tube with Na&03.5H,0 crystals. With Ma valve open to the air, insert the gas chamber of M oin the molten salt, then insert both tubes in water in the Mo box. M o w to stand undisturbed for 15 minutes to reach thermal equilibrium. At the end of this time close the Mo valve so the gas chamber is connected to the manometer (thermometer). The reading should be constant. Now seed the supersaturated N&S2O3.5H10with a single crystal of itself. Note: Can a180 be carried out in icewater. Observations: The thermometer registers a rise of several degrees, as rapid crystallization evolves considerable heat. Dem. 340--Heat of Formation (ZnhJ
Experiment developed by LeRoy G. Hornbeck. T o show: The heat of reaction of Zn
+ I?to form ZnL.
Procedure: Into the test tube put exactly 1.5 g Iz a layer of 0.5 g 20-mesh Zn; on top of this put a crystal of iodine. Place in l M 0 with box filled with water and set M" to read room temperatures. Project. Squirt half a dropperful of water into the test tube, stir water in outer Ma box, and record temperature rise. Observation: Within 10 seconds there is violent reaction; ZnI, is formed; the heat of formation vaporizes some iodine and raises the temperature of the water 5'C. Reference: MARTIN,D. R., J . Chem. Educ., 25, 495 (1948). Dem. 3 4 7-Heat
of Hydration of CaO
Experiment developed by LeRoy G. Hornbeck. To show: Heat of hydration of CaO measured by gas thermometer Ma. Materials: Ma, fresh lumps of CaO, medicine dropper, culture tube. Procedure: Three-quarters fill box Mo with water, and in it a culture tube containing lumps of fresh CaO to a depth of 1 in. Adjust Noto read room temperature, and project. Dump in (CARE: steam may shoot out of tube, avert face) medicinedropper of water. Stir the water in Ma box, using the culture tube as the stirrer. Record temperature change. Observation: The temperature rose 5 T . Reference: STONE,C. H., J. Chem. Educ., 4,630 (1927). Dem. 342-Heat
of Hydration of CuSOa
Experiment developed by LeRoy G . Hornbeck. T o show: A comparison of heat evolved when water is added to CuSOa.5H20and anhydrous CuSO4. Materials: Ma, two culture tubes; anhydrous CuSO4 and CuS04.5Hz0,both powdered to hasten dissolving. Procedure: (a) Repeat Dem. 341, adding 20 ml H20 to 6 g. CuS04.5H,O in place of CaO. (b) Repeat, using 4 g (equivalent amount of anhydrous CuSOn),being sure to add the same amount of Hz0 as in (a). Observations: Mo falls 2'C with the hydrate, rises 13'C with the anhydrous salt, in the case of CUSOI. Note: With BsC1,.2 H,O the fall is 41jn0, and with anhydrous BaCb, the rise is 1'/2T.
Reference: STONE, C. H., J . Chem. Educ., 4, 630 (1927). Volume 43, Number 12, December 7 966 / A 1 0 7 9
