Why Does Hydrogen Peroxide Fizz Only on Wounds?

[DaveC426913]

Been using H_2 O_2 to sterilize a wound. I notice that it fizzes.

1] I presume the bubbles it releases are O_2. i.e. 2 H_2 O_2 > 2H_2 O + O_2
2] I further presume it is the O_2 that kills the bacteria.

And that makes me wonder:
3] I notice that it only fizzes on my wound - it does not fizz when applied to normal skin (or the container it comes in, or the Q-tip). Although it does fizz when poured into the drain. It seems to zero in on organic material.

I am guessing this is because:
- my skin has an oily (i.e. water repellant) coating that the peroxide can't react on/with, or
- the wound has chemically active components that normal skin will not expose, or
- the wound has physically reactive components - like the miscroscopic nicks in a champagne glass that serve as bubble nurseries (I forget the name)

4] Also, why does it not spontaneously revert to water in the bottle? Even over a long time?


Thoughts?

 

[dextercioby]

1.Yes,the reaction u've discribed is incorrect...The correct redox is:

H_{2}O_{2}\rightarrow H_{2}O+O

which means the one atom gets reduced and another oxydated...Note that atomic oxygen is the powerful oxydating agent...So not O_{2} kills bateria (it would be ridiculous,why need hydrogen peroxyde,then),but atomic oxygen...

Daniel.

 

[GCT]

I'm sure this will be sufficient:

http://science.howstuffworks.com/question115.htm

 

[DaveC426913]

Thank you. I don't think I could have gotten a more comprehensive answer if I'd written the question after reading the answer!

P.S. dexter: you might want to read it too. It specifies pretty much the exact reaction I did:

H2O2 --> H2O + O2

(I think your and their answer are ultimately equivalent, you are just concentrating on a discrete intermediate step).

 

[omagdon7]

no actually your equation isn't balanced making it wrong. It is a two step reaction as oxygen isn't going to stick around in its monatomic form for long but if it was immediately just diatomic then the air would be as good a bacteriocide as hydrogen peroxide.