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The Pulsing Reaction

From the Teachers TV series Demonstrating Chemistry, this video shows how to carry out a stunning demonstration of autocatalysis, whereby the products of one reaction act as a catalyst for the next.

Professor Hal Sosabowski mixes hydrogen peroxide, potassium iodate with sulphuric acid and a mixture of malonic acid, starch and manganese sulphate. He spins the solution in a large measuring cylinder to create a vortex to ensure the oscillating reaction occurs throughout the solution. The colourless solution slowly turns amber and then suddenly turns a very dark blue colour. This slowly fades back to a colourless solution and the process repeats. The reaction is known as the Briggs-Rauscher reaction, although there are other similar pulsing reactions.

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