A VERSATILE CLOCK REACTION Submitted by: James L. Dye, Michigan State University, East Lansing Checked by: Twenty MSU Traveling Science Teachers

PREPARATION 2. Mix one volume of A plus one-half volume of B Obtain four beakers or large test tubes, 2-100 ml plus an equal volume of water Note time for appear-

graduates, a thermometer, burner or hot plate, timer, ance of bluecolor. ire the following three solutions: 3 Mix equal volumes of A and B, one of these holu-

tions heme; chilled or heated 20' belom or above room and prep:

Solutii

DEMON: From tim Some of t that they

CATA LY

Claytc Cftliforni in place <

onstratio ' M r d I Hay 195 is partic1

A DEMC

Edgar Buffalo, sti urted side pail W h m I I

In A: -

temperature (this results in an average temperature of potassium iodide, KI change of 10'). Note time for appearance of blue ~g sodium thiosulfate, % & 0 3 color. nl of 5% soluble starch in sufficient water to 4. Mix equal volumes of A and B with one drop of ake 1 liter of solution catalyst added to B Note time for appearance of blue m B. of sodium peroxysulfate, Na~S20g in sufficient ater to make 1 liter of solution. If all of the lid cannot be dissolved, pour off the clear sat- ated solution.

st: nail amount of a dilute aqueous solution of ;SO4 w ith CuS04 in a dropping bottle.

ix equal volumes of Solutions A and B and note a-ppearance of the blue color.

color. REMARKS

This demonstration is most dramatic if solutions A and B are prepared and given to 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 fac- tors discussed in connection with the speed of reactions, temperature, concentration, and effect of a catalyst.

I Rewritten from STEINBACH, OTTO F., AXD KING, CECIL V., 'Exoeriment? in Phvsical Chemistrv." American Book Co. 1950, p 220.

J i a l of Chemical Education Am1 1860

STRATION NOTES e to tzme, items such as the following which do not require a full half page will be listed together hem will be modifications of previously published demonstrations, i n which case it i s suggpsted be clipped and attached to the pertinent experiment.

TIC OXIDATION OF AMMONIA A TIME SAVER

m Berling of Oakland City College, Oakland, a, points out that the use of copper wire gauze af the coiled platinum or copper wire (see dem- n notes THIS JOURNAL, September 1957, and )emonstratton, Number 17-11 THIS JOURNAL, 6) results in a more spectacular display. This ilarly true if the room can be slightly darkened.

>NSTRATION AID

J. Baney of the New Buffalo High School, New Michigan, suggests the use of a backdrop cou- from the peg board type of masonite with one nted white and the other side painted black.

,.sed in conjunction with appropriate hooks or s for the support of exhibits or demonstrations, it y improves visibility for student observers.

When small quantities of solids are required for repe- tition of a demonstration, much time may be saved by weighing out several samples and storing for future use in gelatin capsules. Frequently after one sample has been weighed out and placed in a capsule, sufficient ac- curacy may be obtained by loading additional capsules with a corresponding volume. 'Rapid solution of solids is effected if solids are ground to a fine powder prior to loading. This technique has been used successfully in supplying the Michigan State University Traveling Sci- ence Teachers.

A CORRECTION

Sister Mary Casimir, RSM, has discovered a misprint in the equation given in the connection with the reduc- tion of cupric ion by white phosphorus on page A267, June 1958, of THIS JOURNAL It fehould read' 2P + X u + + + 8H20 = 2H,P04 + 5Cu + 10H+.

Journal a/ Chemical Education A p r i l I960