![]() "Do not do demos unless you are an experienced chemist!" ![]() Please read the following disclaimer carefullyīy continuing to view the descriptions of the demonstrations you have agreed to the following disclaimer. There is an orangish-maroon discoloration of the foam that is characteristic of elemental iodine. This leads me to believe that some of the iodide ion is being oxidized in a side-reaction. Perhaps: The decomposition of hydrogen peroxide is fairly exothermic (-106 kJ/mol), which accounts for the "steaming" of the foam column. It should be noted that oxygen is both oxidized and reduced during this reaction, going from a -1 oxidation state in the peroxide to -2 in water and 0 in elemental oxygen. This is an example of disproportionation. ![]() In this demonstration it is the iodide ion which catalyzes the decomposition. The antiseptic quality of the hydrogen peroxide is due to fact that the high concentration of oxygen which results from the decomposition process is toxic to the anaerobic bacteria that are responsible for infection. In the case of cuts and scrapes, the catalyst is an enzyme called catalase which is present in our tissue. This reaction is particularly effective not only because it is amusing, but any student who has put household 3% hydrogen peroxide on a cut or scrape is familiar with the catalytic decomposition of the substance:
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