168
JOURNAL OF
CHEMICAL EDUCATION
Lecture Demonstrations in General Chemistry' SAUL B . ARENSON University of Cincinnati, Cincinnati, Ohio
19.
DECOMPOSITION OF POTASSIUM CHLORATE CATALYZED BY MANGANESE DIOXIDE%
S
ETUP as in Figure 13. Heat the KC103to above melting. A slow stream of oxygen bubbles rises in the tall cylinder of water. Now remove
that the catalyst dumps into the KCIOs. Despite the fact that the KC103 has cooled down somewhat, a rapid evolution of oxygen occurs -in the presence of the Mn02. The presence of oxygsn in the gas space above the water may be demonstrated with a glowing splint. A variation is to have two tubes, one containing KC103, the other KCIOa MnOl, leading to two cylinders of water. Lighted burners are thrust simultaneously beneath the two tubes. &volution of oxygen commences sooner from the catalyzed mixture.
+
DEFLAGRATING SPOON
MERCURY A4ANOMETER SULFUR
the flame and twist the tube containing the Mn02 so -
' Continued from the November, 1940, issue. ' This and the following demonstration were contributed by
Hubert N. Alyea, Assistant Professor of Chemistry. Princeton University.
20.
GAY-LUSSAC'S LAW OF COMBINING VOLUMES
Setup as in Figure 14. If a one-liter flask is used, and the manometer U-tube set close to the neck, the flask will not topple. Light the sulfur over a burner, and lower into oxygen or air in the flask. When, after a few minutes, the gaseous product has cooled, the mercury levels will be equal. This shows that no change in volume has occurred during reaction; that the reaction is probably
+ 1 volume of 4 +1 volume of SO1 and that SOz, not SOa, is the product of the combustion. 21.
THE RESOLUTION OF CARBONATES IN EXCESS CARBON DIOXIDE'
An unfrosted light bulb is set up in series with a pair of copper electrodes dipping into 40 cc. of distilled water in a 100-cc. beaker. Upon adding 2 cc. of saturated Ba(0H)z solution, the lamp shows good conductance. Carbon dioxide is now bubbled through the solution; the light gradually goes out and then comes on again as the soluble bicarbonate is formed. Lime water can also be used, but is not quite as satisfactory because a saturated solution of CaCO3 conducts better than one of BaCOa. 22.
THE MOTION OF MOLECULES IN GASES
When steel ball bearings, such as are used in the ordinary bicycle, are dropped upon a porcelain plate, or thick glass disc, the balls bounce up and down interestingly. As a second plate, held horizontally, is lowered against the bouncing balls, they rebound with increasing frequency. This demonstrates the increase in frequency of collision (pressure) upon compressing a gas. C
23.
EXPLOSIVE RANGE OF GASES'
Three gastight tin cans open at one end are needed; Campbell soup cans are satisfactory. F i the cans (a) one-tenth, (b) seven-tenths, and (c) three-tenths full of hydrogen; and invert them in a trough of water until needed. Then lift them from the water, admitting air, and cover with several thicknesses of filter paper. Poke a hole in the paper and light each can with a taper at the opening. Cans (a) and (b), which contain mixtures of air with 10 per cent and 70 per cent hydrogen, respectively (upper and lower explosion limits), explode mildly. Can (c), which contains almost an equivalent mixture This and the fallowing demonstration were contributed by A. E. Koenig, Professor of Chemistry, Montana Sehaal of Mines. 'This and the following demonstration were contributed by J. C. Warner, Head of the Department of Chemistry. Carnegie Instituteof Technology.
of hydrogen and oxygen, explodes so violently that it must be kept at arm's length. 24. CHEMICAL KINETIC-REACTION VELOCITY (a) Effect of Catalysts: One of the cans mentioned immediately above should be filled with two parts Hz and one part O*. Here as before the can is kept in the trough until needed. It is removed in the same manner, only this time the filter-paper cover is removed and the can is covered with a large cardboard paddle which has a small ball of platiuized asbestos suspended from the end. The reaction is almost spontaneous. Caution: Stand back-the readion is very violent. (6) Effect of Ternfieratwe: 1. Fifty cc. concentrated H&O4 a t room temperature are poured into 50 cc. saturated sugar solution. 2. Fifty cc. concentrated H&O4 are poured into 50 cc. saturated sugar solution, after both solutions have been cooled 15°C. below room temperature. These reactions are carried out simultaneously. Mount on a ring stand side by side. Place large evaporating dishes under the beakers. 25. COLD PHOSPHOROUS F L d A few pieces of phosphorus are placed in a dry receiver which is filled with glass wool. The receiver is placed in a water bath and a stream of dry Cop is passed through. The phosphorous vapor, carried along with the cG, oxidizes in the air; and a green flame results which is so cool that a finger may be held in it. .. 26. ' w m BLUEPRINTS PRINT@ Take a block of wood about 6" X 6' X I", and near each comer drill a hole large enough to support a 6' X 1' test tube. In the center of the block mount a ~ h o t o flood lamp. Expose the following solutions t o this light for 30 seconds: (a) femc chloride, (b) femc chloride plus citric acid or other suitable reducing acent.. (c) . , same as preceding tube, but shielded from the light with paper, (d) same as preceding tube, but shielded from the light with red cellophane. Now add potassium ferricyanide to each tube. Tube (b) alone gives a test for ferrous iron, indicating that conditions (a), (c), and (d) will not lead to the photoreduction of ferric to ferrous ion. Tube (d) shows that red light cannot cause this reaction and suggests why the photographic dark room has a red "safety" light. Blueprints contain ferric citrate or femc oxalate, and the iron is photochemically reduced to the ferrous condition. Upon dipping the paper into a solution of potassium ferricyanide developer, ferrous ferricyanide (Turnbull's blue) is formed.
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Contributed by W E. Caldwell, Assistant Professor of Chemistv, Oregon State College. Contributed bv G . M. Lisk. Northwestern State Colleae. - . Alva, Oklahoma.
