SPONTANEOUS COMBUSTION Submitted by: John T. Geoghegan and Edward H. Sheers, Arizona Chemical Co., 1937 W. Main Street, Stamford, Conn. 06904 Checked by: Mary Jane Wolf, Hillside Junior High School, Parma, Ohio PREPARATION
Provide 14 g recently purchased boiled linseed oil, 7 g absorbent cotton, 360° thermometer, and an adapt* tion of Mackey'sl spontaneous combustion apparatus, consisting of a 1-gal paint can to he used as a water bath. Inserted in the can is a 1-1 tall form beaker (without a pouring lip) fitted with a 3-hole No. 15 rubber stopper. Two glass tubes, A, about 0.5 in. i.d. X 6 in. long are placed so one tube extends to within 0.5 in. of the bottom of the heaker and the other tube is flush with the bottom of the stopper. These tubes cause a current of air to flow through the beaker. Supported in the beaker is a 6 in. high X 1.5 in. diameter cylinder, B, made of 24-mesh stainless steel gauze. Lead shot supports the cylinder and also supplies weight to keep the beaker from floating. The thermometer extends two inches down into the cylinder. Three holes in the Mackey, W. McD., J . Soc. Chem. Ind, 15,90 (1896). For other spontaneous combustion demonstrations see Spontaneous Combinations in "Tested Demonstrations," by ALYEA, 1%. N., AND DUTTON, F. B., CHEMICAL EDUCATION PUBLISHING Co., Easton, Pa.
can lid are for the beaker, the reflux condenser, and for the periodic addition of water. DEMONSTRATION
The boiled linseed oil is poured onto the cotton which is then wrapped around the thermometer so that the mercury bulb is located in the middle of the roll. The cotton roll is inserted into the wire mesh cylinder, and this assembly is immediately placed in the beaker. CAUTION: Cotton wet with oil is subject to spontaneous combustion and therefore should he handled with care.
11 [I -..-,..
REMARKS
In about one half hour the temperature of the cotton will be over 225'C, while thesurrounding steam is only 10O0C. Upon removal from the apparatus definite evidence of charring can be seen on the cotton. of C h m k d Education
1
Oxidation of Copper by Hydrochloric Acid
May 1068
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Submitted by: Noojin Walker and Donald L. George, Pensacola Junior College, Pensacola, Fla. Checked by: David B. Moss, Hiram College, Hiram, Ohio 44234 PREPARATION
REMARKS
Have available 12F HC1, 15F NHdOH, 0.25 g fine copper turnings freshly washed in cold 12F HCI, two 25-mm test tubes, and a beaker of boiling water.
The activity series of the metals as well as the calculated potentials (Cu 2H+ -+ Cu2+ HZ, -0.34 v), may lead the student to expect that copper cannot be oxidized by HC1. He is likely to overlook the fact that the standard oxidation-reduction potentials require unit activity of the ions. As the concentration changes, however, the relative positions of the halfreactions can he inverted as in this case. Students may be asked to comment on the absence of a blue colored solution as the copper dissolves in the HCI. Excess chloride favors the formation of the tetrachloro complex
DEMONSTRATION
Place the balled copper turnings in the test tube and add 2 ml of 128' HC1. Place the test tube in a beaker of boiling water and heat for at least 3 min. Pour the liquid from the reacting tube into another test tube, cool in ice water, and neutralize very carefully with 15F NH40H. Finally, add an excess of ammonia. The very pale yellow solution will slowly change to light blue as the diammine copper(I1) complex is formed. On standing the blue color gradually deepens.
+
Cu(HAN Blue
+
+ 4C1- e CuCI,*- + 4H,O Yellow
J
l of Chemical Education
May 1968
