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Speaker 1: Welcome to brain Stuff from how Stuff Works dot Com

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Speaker 1: where smart happens. Him Marshall Brain with today's question, why

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Speaker 1: does hydrogen peroxide foam when you put it on a cut?

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Speaker 1: Hydrogen peroxide is something that you buy at the drug store.

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Speaker 1: What you're buying is a three percent solution, meaning the

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Speaker 1: bottle contains water and three percent hydrogen peroxide. It's not

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Speaker 1: bad for washing cuts and scrapes, and the foaming looks cool.

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Speaker 1: The reason why it foams is because blood and cells

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Speaker 1: contain an enzyme called catalase. Since a cut or scrape

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Speaker 1: contains both blood and damaged cells, there's lots of catalase

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Speaker 1: floating around. When the catalase comes in contact with hydrogen peroxide,

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Speaker 1: it turns the peroxide into water and oxygen gas. The

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Speaker 1: bubbles you see contain the oxygen. Catalase accelerates the decomposition

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Speaker 1: of hydrogen peroxide and does this extremely efficiently, up to

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Speaker 1: two thousand reactions per second per molecule of catalase. The

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Speaker 1: bubbles you see in the foam are pure oxygen bubbles

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Speaker 1: being created by the catalase. Try putting a little hydrogen

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Speaker 1: peroxide on a cut potato and it will do the

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Speaker 1: same thing for the same reason. Catalase in the damaged

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Speaker 1: potato cells reacts with the hydrogen peroxide. Hydrogen peroxide does

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Speaker 1: not foam in the bottle or on your skin because

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Speaker 1: there's no catalase to help the reaction to occur. Hydrogen

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Speaker 1: peroxide is stable at room temperature. Do you have any

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Speaker 1: ideas or suggestions for this podcast? If so, please send

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Speaker 1: me an email at podcast at how stuff works dot com.

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Speaker 1: For more on this and thousands of other topics, go

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Speaker 1: to how stuff works dot com.