WEBVTT - Why does hydrogen peroxide foam when you put it on a cut?

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<v Speaker 1>Welcome to brain Stuff from how Stuff Works dot Com

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

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<v Speaker 1>does hydrogen peroxide foam when you put it on a cut?

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<v Speaker 1>Hydrogen peroxide is something that you buy at the drug store.

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<v Speaker 1>What you're buying is a three percent solution, meaning the

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<v Speaker 1>bottle contains water and three percent hydrogen peroxide. It's not

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<v Speaker 1>bad for washing cuts and scrapes, and the foaming looks cool.

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<v Speaker 1>The reason why it foams is because blood and cells

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<v Speaker 1>contain an enzyme called catalase. Since a cut or scrape

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<v Speaker 1>contains both blood and damaged cells, there's lots of catalase

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<v Speaker 1>floating around. When the catalase comes in contact with hydrogen peroxide,

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<v Speaker 1>it turns the peroxide into water and oxygen gas. The

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<v Speaker 1>bubbles you see contain the oxygen. Catalase accelerates the decomposition

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<v Speaker 1>of hydrogen peroxide and does this extremely efficiently, up to

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<v Speaker 1>two thousand reactions per second per molecule of catalase. The

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<v Speaker 1>bubbles you see in the foam are pure oxygen bubbles

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<v Speaker 1>being created by the catalase. Try putting a little hydrogen

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<v Speaker 1>peroxide on a cut potato and it will do the

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<v Speaker 1>same thing for the same reason. Catalase in the damaged

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<v Speaker 1>potato cells reacts with the hydrogen peroxide. Hydrogen peroxide does

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<v Speaker 1>not foam in the bottle or on your skin because

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<v Speaker 1>there's no catalase to help the reaction to occur. Hydrogen

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<v Speaker 1>peroxide is stable at room temperature. Do you have any

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<v Speaker 1>ideas or suggestions for this podcast? If so, please send

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<v Speaker 1>me an email at podcast at how stuff works dot com.

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<v Speaker 1>For more on this and thousands of other topics, go

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<v Speaker 1>to how stuff works dot com.