# If hydorgen peroxide is left in an open container....
**URL:** https://boards.straightdope.com/t/if-hydorgen-peroxide-is-left-in-an-open-container/593046
**Category:** Factual Questions
**Created:** [August 17, 2011, 4:51pm UTC](https://boards.straightdope.com/t/if-hydorgen-peroxide-is-left-in-an-open-container/593046 "2011-08-17T16:51:04Z")
**Posts on this page:** 9
**Page:** 2
### Author:  [@njtt](https://boards.straightdope.com/u/njtt)
#### Post date: [April 25, 2013, 12:46am UTC](https://boards.straightdope.com/t/if-hydorgen-peroxide-is-left-in-an-open-container/593046/21 "2013-04-25T00:46:53Z")
> [@Grinfranklin](#):
>
> Here is my question: I have a favorite knife that I use for EVERYTHING in the kitchen. After each use I rinse and brush it off and put it in a glass with about half hydrogen peroxide and half water. How long should I expect the hydrogen peroxide to be effective in killing the germs or whatever on my knife?
Although the effect might not be immediately obvious, I would expect peroxide to cause rusting of the knife. It is a strong oxidizing agent (unsurprisingly) and I doubt if it is doing your blade any good at all (even if it is supposedly “stainless”). I would look for another way of cleaning it.
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### Author:  [@commasense](https://boards.straightdope.com/u/commasense)
#### Post date: [April 25, 2013, 3:36am UTC](https://boards.straightdope.com/t/if-hydorgen-peroxide-is-left-in-an-open-container/593046/22 "2013-04-25T03:36:36Z")
> [@adianadiadi](#):
>
> Hydrogen peroxide has higher bp than water and hence water is evaporated first leaving behind H2O2, whose conc. increases leading to more collisions between them. This increases the speed of decomposition of H2O2.
Right.
I use a glass of ordinary consumer-grade hydrogen peroxide to sanitize my snoring mouthpiece, and got to wondering how long it would take for the stuff to become ineffective.
So I set out a fresh glass every other day for about ten days, until I had six glasses ranging from 1 to 10 days old. I then tested the reactions I got when I poured the samples on some yeast, a technique I read about on the Web somewhere, since I didn’t have any lab equipment to do more sophisticated tests.
I had expected to get more reaction from the fresher samples and less from the older ones, since I assumed that the stuff would decompose over time.
To my surprise, the results were the opposite: the older samples gave stronger reactions with the yeast. I realized that the water used to dilute it was evaporating, leaving a higher concentration of H[sub]2[/sub]O[sub]2[/sub] behind.
Of course, I can’t say what would happen over a much longer period of time.
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### Author:  [@Pinson](https://boards.straightdope.com/u/Pinson)
#### Post date: [July 11, 2017, 1:35pm UTC](https://boards.straightdope.com/t/if-hydorgen-peroxide-is-left-in-an-open-container/593046/23 "2017-07-11T13:35:29Z")
Yes, a girlfriend took and ancient bottle of H2O2 out of her medicine cabinet. It was marked 3%. But it reacted, killing the surface cells on your hand. Much like 35% food grade H2O2 would do.
The boiling point of water is 212 °F, but the boiling point of H2O2 is 302.4 °F. So the water would disappear first, leaving behind higher amounts of H2O2.
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### Author:  [@Weisshund](https://boards.straightdope.com/u/Weisshund)
#### Post date: [July 11, 2017, 5:23pm UTC](https://boards.straightdope.com/t/if-hydorgen-peroxide-is-left-in-an-open-container/593046/24 "2017-07-11T17:23:09Z")
> [@Pinson](#):
>
> Yes, a girlfriend took and ancient bottle
and applied it on an ancient post 😃
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### Author:  [@Melbourne](https://boards.straightdope.com/u/Melbourne)
#### Post date: [July 12, 2017, 1:57am UTC](https://boards.straightdope.com/t/if-hydorgen-peroxide-is-left-in-an-open-container/593046/25 "2017-07-12T01:57:51Z")
> [@Weisshund](#):
>
> and applied it on an ancient post 😃
Cleaned it up, but I don’t think damaged it at all.
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### Author:  [@davida03801](https://boards.straightdope.com/u/davida03801)
#### Post date: [July 12, 2017, 4:12am UTC](https://boards.straightdope.com/t/if-hydorgen-peroxide-is-left-in-an-open-container/593046/26 "2017-07-12T04:12:46Z")
Just what is the half life of H2O2 ?
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### Author:  [@TriPolar](https://boards.straightdope.com/u/TriPolar)
#### Post date: [July 12, 2017, 2:21pm UTC](https://boards.straightdope.com/t/if-hydorgen-peroxide-is-left-in-an-open-container/593046/27 "2017-07-12T14:21:53Z")
> [@Pinson](#):
>
> Yes, a girlfriend took and ancient bottle of H2O2 out of her medicine cabinet. It was marked 3%. But it reacted, killing the surface cells on your hand. Much like 35% food grade H2O2 would do.
>
> The boiling point of water is 212 °F, but the boiling point of H2O2 is 302.4 °F. So the water would disappear first, leaving behind higher amounts of H2O2.
I have doubts about your conclusion. The problem is that H2O2 breaks down over time releasing oxygen and leaving water behind. Concentrating H2O2 even with controlled distillery is difficult, reaching 35% concentrations just from an old bottle sitting around doesn’t fly. At best the solution left over has a higher than normal concentration of dissolved oxygen, nothing like the concentration of 35% H2O2 though. Even weaker than 3% solutions of peroxide will react with dead skin cells pretty vigorously, 35% would bleach skin very obviously.
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### Author:  [@Isilder](https://boards.straightdope.com/u/Isilder)
#### Post date: [July 13, 2017, 11:44am UTC](https://boards.straightdope.com/t/if-hydorgen-peroxide-is-left-in-an-open-container/593046/28 "2017-07-13T11:44:32Z")
I don’t think the O2 concentrations above the water would produce H2O2 in neutral or hydroxide ,pH \> 7, water.
In neutral, or ph\> 7 clean water (no catalyst) Peroxide does SLOWLY break down.
But it seems that in the water with pH \< 7, peroxide is stable. The lack of dependency on temperature seems to suggest that its simply stable , and neither is peroxide breaking apart, nor being made.
With the break down rate being so slow, le chateliers doesn’t seem to be relevant, its not a reaction that le chateliers is in control of… there isn’t the forward and backward reaction happening.
… Dissolving O2 into water is not a way to make perodixe.
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### Author:  [@whitetho](https://boards.straightdope.com/u/whitetho)
#### Post date: [July 16, 2017, 2:19pm UTC](https://boards.straightdope.com/t/if-hydorgen-peroxide-is-left-in-an-open-container/593046/29 "2017-07-16T14:19:24Z")
Two chemists take a break for lunch. One says “I’ll have a glass of H20” The other says, “I’ll have a glass of H20, too”. Only one chemist returns to work that afternoon.
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