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#1
Old 08-17-2011, 12:51 PM
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If hydorgen peroxide is left in an open container....

If a retail concentration hydrogen peroxide is left in an open container does it decompose and evaporate or react with something and evaporate or just or evaporate ... or what?
#2
Old 08-17-2011, 01:15 PM
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It will slowly decompose, giving off oxygen and leaving water, which, of course, will itself evaporate eventually.

Actually, I doubt that closing the container does very much to slow down the decomposition (although dust particles getting in the open top may speed it up a little), but it will stop the water evaporating.

Last edited by njtt; 08-17-2011 at 01:17 PM.
#3
Old 08-17-2011, 02:44 PM
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Quote:
Originally Posted by njtt View Post
It will slowly decompose, giving off oxygen and leaving water, which, of course, will itself evaporate eventually.

Actually, I doubt that closing the container does very much to slow down the decomposition (although dust particles getting in the open top may speed it up a little), but it will stop the water evaporating.
Well, if sealing the container raises the partial pressure of oxygen in the headspace above the liquid then it should slow the decomposition reaction. Le Chatelier's principle and all that.
#4
Old 08-17-2011, 03:00 PM
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This strikes me almost as homework help, but I'll see if I can move the answer forward.

If it is left in an open container that isn't opaque and the container is left in UV light, it will decompose much faster. The reason hydrogen peroxide is sold in brown bottles is to prevent the reaction that produces water and oxygen from being accelerated by light.
#5
Old 08-17-2011, 03:21 PM
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So ... if I have a 5-year-old bottle of hydrogen peroxide in my medicine chest, that bottle is probably filled with water by now?
#6
Old 08-17-2011, 03:43 PM
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Originally Posted by bordelond View Post
So ... if I have a 5-year-old bottle of hydrogen peroxide in my medicine chest, that bottle is probably filled with water by now?
Correct, it's gone from mostly water to almost exclusively water.
#7
Old 08-17-2011, 03:44 PM
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Originally Posted by randomface View Post
This strikes me almost as homework help, but I'll see if I can move the answer forward.

If it is left in an open container that isn't opaque and the container is left in UV light, it will decompose much faster. The reason hydrogen peroxide is sold in brown bottles is to prevent the reaction that produces water and oxygen from being accelerated by light.
If you really want to speed it up transition metals work best. Manganese dioxide works great at this.
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Old 08-17-2011, 04:05 PM
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Thanks. BTW, back when I was doing homework I would not have needed your help but half a century or more rather dulls the thinking a bit. I once read somewhere that geezers and students often write questions a similar linguistic style but I forgot where I read that.
#9
Old 08-17-2011, 05:25 PM
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If you really want to speed it up transition metals work best. Manganese dioxide works great at this.
I've heard that silver is best. IIRC, the jetpack you sometimes see at big events is powered by silver-catalyzed decomposition of hydrogen peroxide.
#10
Old 08-17-2011, 05:32 PM
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Sorry for the semi-accusation. I saw your name with two questions that seemed similar to a question I got from my younger sister last semester asking for chemistry help.
#11
Old 08-17-2011, 06:24 PM
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From my own anecdotal evidence, this is correct:
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Originally Posted by Bill Door View Post
Well, if sealing the container raises the partial pressure of oxygen in the headspace above the liquid then it should slow the decomposition reaction. Le Chatelier's principle and all that.
And this is incorrect:
Quote:
Originally Posted by bordelond View Post
So ... if I have a 5-year-old bottle of hydrogen peroxide in my medicine chest, that bottle is probably filled with water by now?
Quote:
Originally Posted by Bill Door View Post
Correct, it's gone from mostly water to almost exclusively water.
I had at least 8 year old bottles of hydrogen peroxide in brown bottles stored in a moderately dark place that still displayed notable and impressive reactivity when put in contact with living tissue/blood.
#12
Old 08-17-2011, 08:06 PM
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Amines including the amino end of an amino acid also accelerate decomposition. Heat also.
#13
Old 08-17-2011, 08:15 PM
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Quote:
Originally Posted by Bill Door View Post
Well, if sealing the container raises the partial pressure of oxygen in the headspace above the liquid then it should slow the decomposition reaction. Le Chatelier's principle and all that.
Only if the decomposition is reversible. I doubt it is. Even if it is, LCP doesn't tell us that the forward reaction slows, but that the reverse reaction speeds up. The net result is the same though.


Does this dilute solution contain an inhibitor? The 30% stuff I use in lab does, but I don't know about the solutions sold in stores.
#14
Old 08-17-2011, 09:33 PM
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I had a chemical reference book at school that said commercial hydrogen peroxide solutions are chemically inhibited against spontaneous decomposition, and therefore are stable if uncontaminated. I just poured some from a bottle opened before 2004 onto my finger and also into the bathroom sink. It fizzed quite righteously under my fingernail and on the sink stopper. There's definitely some peroxide left in there.

By the way- for all the tooth bleachers out there- I looked up carbamide peroxide (the active ingredient in tooth bleaching products) in that book. The entry said "see urea peroxide".
#15
Old 08-17-2011, 11:31 PM
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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.

The dust particles also speed up the decomposition.
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#16
Old 08-18-2011, 01:13 AM
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Originally Posted by california jobcase View Post
I had a chemical reference book at school that said commercial hydrogen peroxide solutions are chemically inhibited against spontaneous decomposition, and therefore are stable if uncontaminated. I just poured some from a bottle opened before 2004 onto my finger and also into the bathroom sink. It fizzed quite righteously under my fingernail and on the sink stopper. There's definitely some peroxide left in there.

By the way- for all the tooth bleachers out there- I looked up carbamide peroxide (the active ingredient in tooth bleaching products) in that book. The entry said "see urea peroxide".
That's what I was led to believe, too. In fact, I'm pretty sure one bottle I had actually mentioned a 0.1% belonging to a preservative of some sort.
#17
Old 08-18-2011, 01:11 PM
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Originally Posted by Ruken View Post
The 30% stuff I use in lab does ...
My assumption is "no", but I'll ask anyway:

Can that 30% stuff be used on cuts and scrapes if applied very carefully? Not poured on, but maybe a few drops applied to a cotton swab? Or is it just too caustic at 30% solution?

I always forget that household hydrogen peroxide is heavily diluted
#18
Old 04-24-2013, 08:29 PM
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Cleaning my favorite knife

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?
#19
Old 04-24-2013, 08:33 PM
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if you wash the knife with soap and water it will kill germs. washing washes off germ food and kills germs that a rinse and soak likely won't do.
#20
Old 04-24-2013, 08:37 PM
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Quote:
Originally Posted by bordelond View Post
My assumption is "no", but I'll ask anyway:

Can that 30% stuff be used on cuts and scrapes if applied very carefully? Not poured on, but maybe a few drops applied to a cotton swab? Or is it just too caustic at 30% solution?

I always forget that household hydrogen peroxide is heavily diluted
I missed this back in 2011, but I wouldn't put this stuff on you. It hurts and kills the skin it touches.
#21
Old 04-24-2013, 08:46 PM
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Originally Posted by Grinfranklin View Post
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.
#22
Old 04-24-2013, 11:36 PM
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Originally Posted by adianadiadi View Post
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 H2O2 behind.

Of course, I can't say what would happen over a much longer period of time.
#23
Old 07-11-2017, 09:35 AM
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Boiling point of Water and H2O2

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.
#24
Old 07-11-2017, 01:23 PM
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Originally Posted by Pinson View Post
Yes, a girlfriend took and ancient bottle
and applied it on an ancient post
#25
Old 07-11-2017, 09:57 PM
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Originally Posted by Weisshund View Post
and applied it on an ancient post
Cleaned it up, but I don't think damaged it at all.
#26
Old 07-12-2017, 12:12 AM
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Just what is the half life of H2O2 ?
#27
Old 07-12-2017, 10:21 AM
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Quote:
Originally Posted by Pinson View Post
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.
#28
Old 07-13-2017, 07:44 AM
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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.
#29
Old 07-16-2017, 10:19 AM
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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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