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The ‘Old Nassau’ or Halloween clock reaction
In association with Nuffield Foundation
Source: © Shutterstock
Illustrate dramatic colour changes as a result of redox and precipitation reactions in this vivid demonstration. Includes kit list and safety instructions.
In this experiment, based on the ‘Old Nassau’ or ‘Halloween’ clock reaction, students observe as a mixture containing iodate(V) ions, hydrogensulfate(IV) (hydrogensulfite) ions, mercury(II) ions and starch suddenly turns orange after a few seconds, forming a precipitate of mercury(II) iodide.
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