Demonstration Notes
(J Chem Bd6?.H!JIIB
From time to time items such as the following which do not require a full half-page, will be listed together. Some of them will be modifications of previou sly published demon stration s, in which case it is suggested that they be clipped and attached to the pertinent experimen t .
Resazurin-Reduction
and O xi dation
Philip S. Chen, Atlantic Union College, South Lan caster, Mass. 01561, sub:rhitted the following demon . stration . (See "Methylene Blue-Reduction and Oxidation," DUTTON,F. B. "Chem Ed Tested Demonstration," (6th Ed.), Chemical Education Publishing Co., Easton, Pa., (1965), p. 187.) Dissolve 8 g of potassium hydroxide in approximately 300 ml of water in a 500-ml flask. Allow to cool, and then dissolve 10 g of glucose in the solution. Add resazurin solution (0.1 g in 100 ml of water) dropwise until the· solution appears a fluorescent reddish blue, which then turns to a fluorescent red in less than 2 min, and to colorless in another minute. After the solution becomes colorless, give the flask a slight shake, whereupon the red color returns. On standing for a few minutes, the red will disappear. The color change is spectacular, and resazurin is very sensitive to oxidation and reduction. Conductiv ity of Fused Salts
R. J. Swan, Bar Ilan Secondary School, Netanya, Israel submitted the following improvement for this demonstration described in "Tested Demonstrations in Chemistry," Chemical Education Publishing Co ., Easton, Pa., 1965, p. 164.
In order to reduce the "difficulty (that) may be experienced in maintaining contact .. . " the following innovation is suggested. Grind two carbon electrodes from dry cells until about 1/2cm will fit into the short piece of glass tubing. These electrodes are mounted on two separate retort stands and thus support the glass tubing. Burning Hydrogen
Peter Lewis, Trinity College School, Port Hope, Ontario, Canada, suggests the following improvement for the demonstration in which the flame from hydrogen gas burning at a jet impinges on a glass beaker. The resulting ,rnter is to condense and run down the beaker. If the beaker is replaced by a large piece of aluminum metal the demonstration is more effective, since aluminum is a good conductor of heat, and remains relatively cool. Burning Sugar
Joseph E. Johnston, Eastern District High School, Brooklyn, New York, 11211, tells us, "that the flame of an ordinary match will not cause a sugar cube to ignite. If rubbed with cigarette ash and a match is then applied, the sugar will burn with a blue flame. Is the ash a catalyst or does it produce a wick effect"? JouRNAL
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of CHEMICAL
EDUCATION
· APRIL
1970
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( J Chem Bd6?.H!JIIB
I I Submitted by: Phillip S. Chen, Atlantic Union Coliege, South Lancaster, Mass. 01561 I I Tested by: Adele Hoskin and Dale Dreisbach, Hiram College, Hiram, Ohio 44234 I The green color can be restored quickly by vigorously PREPARATION shaking the solution. Alternatively, the various colors Prepare the following stock solutions I can be restored one by one in reverse order by shaking A. 4 g KOH dissolved in 150 ml water and allowed to the solution gently at first and then more vigorously. cool to room temperature This experiment can be repeated a number of times. B. 5 g glucose in 150 ml water When the green color fades add more indicator (D). C. 0.1 g benzoin dissolved in 100 ml methanol D. 0.5 g indigo carmine dissolved in 100 ml water
I
DEMONSTRATION
In a large test tube provided with a stopper, mix 10 ml of A and 10 ml of B. To this add 1.5 ml of C and 12 ml of C. The blue color of the indicator (D) changes instantly to green. After a certain induction period, the green will rapidly change to purple, then red, orange, and finally yellow.
REMARKS
Indigo carmine, an oxidation -reduction indicator, is reduced by an alkaline glucose solution from green to the yellow. On shaking with air the reduction product is reoxidized to green. The color changes take place more slowly without benzoin.
Volume 47, Number 4, April 1970 / A3~5
