Hydrogen Peroxide

why does it bubble? and why does it get warm?

Hydrogen peroxide is H[sub]2[/sub]0[sub]2[/sub]. It’s fairly unstable and when it reacts with dirt and oils on the skin it releases oxygen gas, thus the bubbling. It also releases some energy in the form of heat. What’s left when the bubbling stops is water.

that is weird.

No, that is chemistry!

It’s really no weirder then the concept that igniting hydrogen gas produces water.

chemistry is weird. and i want nothing to do with it other than to pass high school next year. i want nothing to do with the chemistry teacher either, but don’t tell her i said that.

Glad we’re here fighting ignorance while indirectly supporting your desire to remain so.

You can’t avoid chemistry. You are chemisty.

Not really. If you put it on your plain skin, even if it’s dirty, it doesn’t bubble much. The main reason it bubbles is because of the presence of the enzyme catalase. That’s why it bubbles when there’s a cut (blood and cells contain catalase) and when you gargle it in your mouth.

How stuff works article: Why does hydrogen peroxide foam when you put it on a cut?

This is an important and simple test in bacteriology. When you’re trying to figure out what bacteria you’re looking at, knowing whether it makes catalase or not is useful information. So just drop some H2O2 on a colony and see if it bubbles.

And when you add H202 to a wound you’re killing bacteria which does not have catalase, helping to prevent infection. The bubbling you see is usually from your very own human catalase.

High school science teacher chiming in: We have catalase in our cells because hydrogen peroxide is a waste product of metabolism. The catalase catalyzes the breakdown of hydrogen peroxide to water and oxygen (which makes the bubbles you see). My students do a lab exercise wherein they qualitatively measure the catalase activity of different tissues under different conditions (boiling, ground-up to increase surface area, etc.) It’s a fun lab…I enjoy grossing the kids out by making them grind up raw liver.:stuck_out_tongue:

I put my earrings into hydrogen peroxide to clean them, and wait until it stops bubbling. Is this actually helping me prevent infections in my piercings?

Does this mean it selectively kills non-human cells, or just that both types of cells die, and only human cells produce bubbles? Is H2O2 effective against bacteria that produce catalase?

Yes, it is. Typically, you’ll put much more of it on the bacteria than they can handle.

Science is not weird, science is awesome. Science brought you this message board. This post is sponsored by the element Si.

You can also make H[sub]2[/sub]O[sub]2[/sub] decompose very quickly, which is quite dramatic. I think manganese dioxide was used, but it was a very long time ago.

Hydrogen peroxide was also used as an oxidizer in early rocket engines, such as those of the Nazi V2 rockets. It’s extremely dangerous to handle, and there were several instances of rockets exploding because of spilled oxidizer mixing with the fuel. There were also some experimental engines using H[sub]2[/sub]O[sub]2[/sub] as a fuel – mostly for submarines, but this was also very dangerous.

More recently, H[sub]2[/sub]O[sub]2[/sub] has been used as a propellant in the Russian Shkval high-speed torpedoes. The explosion of such a torpedo – followed by the explosion of other torpedoes containing H[sub]2[/sub]O[sub]2[/sub] in the subsequent fire – is believed to have caused the sinking of the Kursk in 2000.

H[sub]2[/sub]O[sub]2[/sub] is used as a rocket fuel but not in the normal sense of the word. Whe it’s squirted onto a metal catalyst, platynum IIRC, it reacts and the resulting volume of gas and water vapor worked just as well as burning fuel and oxidizer. I know it was commonly used for attitude control systems.

Note that drugstore grade hydrogen peroxide is only 2% with perixide for bleaching hair maybe twice that.

You are correct that H[sub]2[/sub]O[sub]2[/sub] has been used as a monopropellant for rockets, using catalytic decomposition. It decomposes to oxygen and water, with enough energy released for the water to be vaporised. It is convenient for attitude control because the thrust can be easily switched on and off, and the peroxide can be stored indefinitely.

However, it is also an oxidiser in itself, and can function as the oxidiser in a bipropellant rocket. So it can be a rocket fuel in the “normal sense of the word”, although personally I like to restrict the term “fuel” to the reducing agent rather than the oxidising agent.