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Author: Subject: Air pump to replace H2O2?
CHRIS25
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[*] posted on 10-5-2012 at 00:52
Air pump to replace H2O2?


Could one use a fish tank air pump to replace the need for adding hydrogen peroxide in order to deliver oxygen into a solution? I saw one guy using it on a demonstration, but he did not say or describe why and there was no mention of it replacing the need for H2O2 in order to keep o2 levels constant.

(this is referring to the Copper and Hcl reaction mentioned in a previous thread).

Thanyou.




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weiming1998
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[*] posted on 10-5-2012 at 01:31


Quote: Originally posted by CHRIS25  
Could one use a fish tank air pump to replace the need for adding hydrogen peroxide in order to deliver oxygen into a solution? I saw one guy using it on a demonstration, but he did not say or describe why and there was no mention of it replacing the need for H2O2 in order to keep o2 levels constant.

(this is referring to the Copper and Hcl reaction mentioned in a previous thread).

Thanyou.


You can do that, but it would be extremely slow, in the order of days or even weeks, to dissolve the copper. That is because of the ridiculously low solubility of oxygen in water, especially HCl gas-saturated water. Copper also reacts slowly with oxygen, unlike H2O2, which is the more reactive source of oxygen with a O-O single bond, which is easier to break. I personally would not attempt the air pump. You can try another source of oxygen though, like persulfates, which are used for etching themselves, though I would use H2SO4 instead of HCl to go with that (HCl is mildly reducing)
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[*] posted on 10-5-2012 at 01:54


Actually, things are not as bad as weiming1998 tells. Once you have a little Cu(2+), then things become much easier. Metallic copper easily dissolves in conc. HCl, in which also Cu(2+) is present. Such solutions are very dark, almost black, due to mixed oxidation state copper(I)/copper(II) chloro complexes. These complexes in turn are very air sensitive and they really suck oxygen from the air.

So, you can start with conc. HCl to which a small amount of H2O2 is added and then add copper to that. This gives you an initial amount of Cu(2+), in the form of the green/brown CuCl4(2-) complex. Once you have this, you can dissolve additional copper fairly easily, using oxygen from the air. You then can keep some of your copper(II) containing solution for future sessions in which you want to dissolve more copper. You only need to assure that the solution remains sufficiently acidic, so you need to top up with fresh HCl when a decent amount of copper has dissolved.

One point to keep in mind is that the solution is very corrosive and bubbling air through this takes away fumes of HCl and these are very nasty. Everything nearby becomes humid and metals nearby will rot and rust away as if they are in hell. So, do this outside or in a very well-ventilated room.




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AndersHoveland
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[*] posted on 10-5-2012 at 03:10


30% concentrated sulfuric acid and some potassium nitrate will also gradually dissolve copper. It takes about 20 minutes before the reaction really becomes apparent, and about 1-2 hours to fully dissolve.

One comment, while copper certainly will slowly dissolve in acids if air is passed into the solution, this tends to be very slow (several hours). Hydrogen peroxide makes the reaction go much faster. It should also be remembered that the presence of chloride ions can significantly alter the chemistry of copper ions, because the CuCl2[-] ion is favorable.

Another option, if one wants to generate a stream of oxygen gas, is to react H2O2 with hypochlorite bleach.

[Edited on 10-5-2012 by AndersHoveland]
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weiming1998
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[*] posted on 10-5-2012 at 04:09


Quote: Originally posted by woelen  
Actually, things are not as bad as weiming1998 tells. Once you have a little Cu(2+), then things become much easier. Metallic copper easily dissolves in conc. HCl, in which also Cu(2+) is present. Such solutions are very dark, almost black, due to mixed oxidation state copper(I)/copper(II) chloro complexes. These complexes in turn are very air sensitive and they really suck oxygen from the air.

So, you can start with conc. HCl to which a small amount of H2O2 is added and then add copper to that. This gives you an initial amount of Cu(2+), in the form of the green/brown CuCl4(2-) complex. Once you have this, you can dissolve additional copper fairly easily, using oxygen from the air. You then can keep some of your copper(II) containing solution for future sessions in which you want to dissolve more copper. You only need to assure that the solution remains sufficiently acidic, so you need to top up with fresh HCl when a decent amount of copper has dissolved.

One point to keep in mind is that the solution is very corrosive and bubbling air through this takes away fumes of HCl and these are very nasty. Everything nearby becomes humid and metals nearby will rot and rust away as if they are in hell. So, do this outside or in a very well-ventilated room.



But an alternate oxygen source is much better and more straightforward, just adding an oxidant to an acid instead of constantly bubbling oxygen/air into HCl for hours on end.

If the acid was changed, lots of different oxidants added to the acid would work in dissolving copper. Examples are nitrates, chlorates (dilute solution), perchlorates, hypochlorites (weak acid!), permanganates, persulfates, peroxymonosulfates, and more.

Edit: The small amounts of Cu2+ ions formed will halve the reaction time at the most, and will not speed up the reaction more than that.

[Edited on 10-5-2012 by weiming1998]
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woelen
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[*] posted on 10-5-2012 at 05:26


My suggested method works MUCH better than by simply halving the reaction time. The more Cu(2+) you get, the faster the reaction goes. In fact, this is a well-known and working practice, used by electronics hobbyists who want to etch copper from printed circuit boards and have no ferric chloride available. Once you have some copper(II) you get more and more of this and the only chemical you really need to replenish is HCl. The rest comes from air. The only problem is to get started, you need either a small quantity of some oxidizer or a small amount of copper(II) to bootstrap the process.

This only works for HCl and HBr, not for other acids. The reason for this is that the chloro (and bromo) complexes strongly affect the chemistry of copper(I) and copper(II) and especially the following reaction becomes very favorable:

CuCl4(2-) + Cu --> 2CuCl2(-)

The formed copper(I) in turn is very easily oxidized by oxygen (it really sucks oxygen into solution, it is very eager to react and everywhere where the liquid is in contact with air it quickly absorbs oxygen). In this process additional chloride and acid is consumed, water and chloro-complex of copper(II) being formed.

Similar reactions also occur with bromide instead of chloride. Other anions like sulfate, nitrate, perchlorate do not show such behavior and indeed, dissolving copper metal in dilute aqueous solutions of these acids is slow, very slow, because absorption of oxygen from the air by the solutions is very slow due to the low solubility of the oxygen.




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[*] posted on 10-5-2012 at 05:28


It works. People use it as printed circuit board etchant.
http://www.goldrecovery.us/goldrecovery/documents/CuCl.pdf
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CHRIS25
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[*] posted on 10-5-2012 at 05:37


Gentlemen, very helpful, even the slight differences of opinions I can actually learn from. Point taken about doing it outside I really would not have known that bit. Grateful to all.
Kind regards.




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[*] posted on 10-5-2012 at 08:39


I've done it - dissolved something like 100 pre-1982 US pennies (98% copper) using an aquarium air bubbler and concentrated HCl. I had a window exhaust fan to direct fumes outside, along with a lid on the coffeepot I was using, and the fumes still did some damage to exposed steel in the area.
It does take a while, though, even at higher temperatures. As woelen notes, it speeds up once you actually have a decent amount of CuCl2 in solution.




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[*] posted on 11-5-2012 at 02:27


same thing goes for PbCl2

adding 32%HCl to lead powder and bubbling for a few days dissolves the lead quite rapidly, and it is replaced with a white powder.

Li
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CHRIS25
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[*] posted on 11-5-2012 at 04:50


Mmm this certainly seems a great way to cut down on very expensive peroxide (@ 12 - 14 dollars for 1 litre 6%) However I can not safely extract the fumes even outside would be risky but the knowledge about all this may prove useful in the future.



‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)

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[*] posted on 11-5-2012 at 06:50


I have used a air pump to successfully produce ferric chloride from iron and HCL it took about a week outside in the sun.
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CHRIS25
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[*] posted on 11-5-2012 at 07:11


Yes - PERTH! Lucky you. Today is a sunny day, blue skies and gentle wind. Yet it has rained three times already. This is what it is like every day here, yep you don't even need a cloud in Ireland for it to rain. I think I will buy a chimney:)



‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)

The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by precision and law. (me)
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