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Name: Larry
Status: other
Grade: N/A
Location: TX
Country: N/A
Date: August 2006

Question:
Which liquid chemicals when mixed cause them to continuously change colors?

I attended a seminar in which a chemist, just for show, mixed and vigorously stirred different liquid chemicals into a large clear, colorless beaker. After he finished, the colorless liquid in the beaker changed color. It changed later to another color, then another color. He never added anything during these changing of colors. All the while, the mixture was still swirling slowly in the beaker. I want to know what chemicals or liquid chemicals are needed to give this kind of visual color changes (or reactions). He did not tell us what the chemicals were because he did not want to give away his "secrets."



Replies:
Larry,

These reactions are generally called "clock reactions" and there are many particular chemicals that can be used to product clock reactions. One, called the Briggs-Raucher reaction, uses hydrogen peroxide, potassium iodate, malonic acid, manganese sulfate, sulfuric acid and starch. It will be particularly difficult for you to find malonic acid because it is a DEA restricted chemical due to its ability to synthesize certain narcotics. The easiest one to set up that I found (just Google clock reactions) involves sodium thiosulphate, potassium iodide, starch and hydrogen peroxide. This link will help you set things up if you want to do it yourself:

http://www.science.demon.co.uk/handbook/25.htm

The basic premise of clock reactions is that you have two reactions involved in a "tug-of-war". One reaction will consume starting materials and produce a certain color and byproduct. That byproduct is the starting material for the other reaction, which produces a different color. This process is cyclic in nature and usually will go on for many cycles until other impurities are formed and no more staring materials are being formed, or the reaction is quenched. Google either "clock reactions" or "Briggs Raucher reaction" for more information.

Matt Voss


I am not sure why the lecturer was reluctant to "give away his 'secrets'" since there are no secrets. There are numerous chemical reactions that undergo color changes "by the clock". If you do a "Google" search on the term "clock reactions" you will find many such reactions, as well as other reactions that oscillate back and forth between various colors. For starters try:

http://science.csustan.edu/Stkrm/Recipes/Recipes-Contents.htm

Vince Calder



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