A VERSATILE CLOCK REACTION Submitted by: James L. Dye, Michigan State University, East Lansing Checked by: Twenty MSU Traveling Science Teachers PREPARATION
Obtain four beakers or large test tubes, 2-100 ml graduates, a thermometer, burner or hot plate, timer, and prep:ire the following three solutions: SolutiiIn A : of potassium iodide, KI ~gsodium thiosulfate, % & 0 3 nl of 5% soluble starch in sufficient water to ake 1 liter of solution
m B. of sodium peroxysulfate, Na~S20gin sufficient ater to make 1 liter of solution. If all of the lid cannot be dissolved, pour off the clear satated solution. st: nail amount of a dilute aqueous solution of ;SO4w ith CuS04in a dropping bottle. ix equal volumes of Solutions A and B and note a-ppearanceof the blue color.
2. Mix one volume of A plus one-half volume of B plus an equal volume of water Note time for appearance of bluecolor. 3 Mix equal volumes of A and B, one of these holutions heme; - chilled or heated 20' belom or above room temperature (this results in an average temperature change of 10'). Note time for appearance of blue color. 4. Mix equal volumes of A and B with one drop of catalyst added to B Note time for appearance of blue color. REMARKS
This demonstration is most dramatic if solutions A and B are prepared and given t o four separate students who mix them simultaneously in front of the class. This clock reaction has the advantage over others in that it is possible to demonstrate all of the common factors discussed in connection with the speed of reactions, temperature, concentration, and effect of a catalyst. I Rewritten from STEINBACH, OTTO F., AXD KING,CECILV., 'Exoeriment? in Phvsical Chemistrv." American Book Co. 1950,
p 220. J i a l
of Chemical
Education
Am1 1860
DEMON:STRATION NOTES From tim e to tzme, items such as the following which do not require a full half page will be listed together Some of them will be modifications of previously published demonstrations, i n which case it i s suggpsted that they be clipped and attached to the pertinent experiment. CATA LYTIC OXIDATION OF AMMONIA
A TIME SAVER
When small quantities of solids are required for repeClaytcm Berling of Oakland City College, Oakland, tition of a demonstration, much time may be saved by Cftlifornia, points out that the use of copper wire gauze weighing out several samples and storing for future use in place NSTRATION AID ence Teachers. Edgar J. Baney of the New Buffalo High School, New Buffalo,Michigan, suggests the use of a backdrop cousti urted from the peg board type of masonite with one side pailnted white and the other side painted black. W h m I,.sed I in conjunction with appropriate hooks or s for the support of exhibits or demonstrations, it y improves visibility for student observers.
A CORRECTION
Sister Mary Casimir, RSM, has discovered a misprint in the equation given in the connection with the reduction of cupric ion by white phosphorus on page A267, June 1958, of THIS JOURNALIt fehould read' 2P X u + + 8H20 = 2H,P04 5Cu 10H+.
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Journal a/ Chemical Education
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A p r i l I960
