Oscillating Clock

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The Oscillating Clock Reaction is a variation of the iodine clock in which the solution cycles between two colors (black and amber). The chemistry is rather complex, but the value in this demonstration is pure entertainment.

The history of the oscillating reaction is interesting. W.C. Bray in 1921 reported an oscillating reaction involving hydrogen peroxide and iodate. It didn’t receive a lot of interest because of experimental difficulties. B.P. Belousov, a chemist in the USSR, discovered a variation this reaction in 1950 using cerium and bromate. His attempt to publish his results was rejected because the reaction did not fit in accepted theory. Later, in 1961, A. M. Zhabotinsky a graduate student in Moscow State University, worked out the details of the reaction. Their work was eventually recognized, and they were recipients of the Lenin Prize in 1980.

In 1973, Thomas Briggs and Warren Rauscher, science instructors at Galileo High School in San Francisco, changed the conditions of the Bray reaction to shorten the oscillating times and made the reaction more visible. The Briggs-Rauscher reaction is the most popular oscillating clock demonstration.

Because the system does not appear to reach equilibrium, it led to an area of interest called “non-equilibrium thermodynamics”. A Belgium chemist, Ilya Prigogine, received the 1977 Nobel Prize in Chemistry for his work on this subject.

As with our “eye-catching” demonstrations, it’s fun to watch the audience as the oscillations occur. In fact, before we go on to other demonstrations, we have to place the beaker behind the stage.

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