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Author: Subject: Precipitated copper powder
The_Davster
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[*] posted on 4-9-2005 at 12:49


I have been doing some more experiments with the reaction between ascorbic acid and CuSO4 recently. I have pure acsorbic acid now, so no more problems with purity:P.
Using 5g vitC and 10g CuSO4, a dark precipitate of copper powder is produced(much more than in my previous experiments). However it takes a long time to settle. The green solution left over is what I have mainly been experimenting with.
1. Green solution +NaOH results in an orange/yellow precipitate.
2. Green solution + HNO3 results in a solution the normal Cu2+ colour(light blue)
3. Solution produced in 2 +NaOH results in the same precipitate as in 1
4. Green solution + Zn results in a black precipitate and bubbling (the most confusing result so far)
5. Green solution +Na2CO3 results in a green precipitate

[Edited on 4-9-2005 by rogue chemist]




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[*] posted on 4-9-2005 at 18:10


1. Cu2O.
2. NO3- oxidizes to Cu++.
3. This suggests it isn't Cu(I) leftover in 1. Maybe the ppt is a complex?
4. How acidic is the solution, and pure the Zn? Most of the time when I'm dissolving Zn it leaves a black colloid, probably copper and other insoluble constituents of the 90% alloy.
5. Malachite?

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The_Davster
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[*] posted on 4-9-2005 at 18:23


It is pure zinc powder and I have never gotten any black matter while dissolving zinc. Also the hydroxide ppt looks nothing like Cu2O, way too yellow.



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[*] posted on 4-9-2005 at 20:14


You sure? That's what I thought first time I made Cu2O. It starts almost yellow then runs to orange then red as the crystals grow, if they continue growing.

Ok, pure zinc? No idea on that!

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[*] posted on 5-9-2005 at 01:02


Quote:
Using 5g vitC and 10g CuSO4, a dark precipitate of copper powder is produced(much more than in my previous experiments). However it takes a long time to settle.

Are you sure it is copper and not some copper (I) compound (e.g. impure Cu2O)? Add some of this dark stuff to dilute HCl. If it is copper it will not dissolve, otherwise it may become white and eventually will dissolve.


Quote:
The green solution left over is what I have mainly been experimenting with.
1. Green solution +NaOH results in an orange/yellow precipitate.
2. Green solution + HNO3 results in a solution the normal Cu2+ colour(light blue)
3. Solution produced in 2 +NaOH results in the same precipitate as in 1
4. Green solution + Zn results in a black precipitate and bubbling (the most confusing result so far)
5. Green solution +Na2CO3 results in a green precipitate


1. Indeed Cu2O, possibly in a hydrous form.

2. The blue color is due to Cu(2+), but certainly not all copper is oxidized to the +2 oxidation state. I doubt whether the HNO3 is oxidizing it, unless it is very concentrated. Usually oxygen from the air oxidizes the stuff. Copper (I) is colorless and copper (II) is blue. In nitric acid and sulphuric acid, the mix also is blue. In hydrochloric acid, however, you'll get deep brown, almost black complexes of mixed valency (cations, with multiple copper ions in it, and with an oxidation state both of +1 and +2 in a single cation). I have done quite some research on copper chemistry and put all my findings on my website, see this link
Another observation I have made is that copper (I) complexes seem to reverse react in strongly acidic environments, which are not coordinating to copper (I), such as nitric acid or sulphuric acid solutions. Copper (II) ions and ascorbic acid can coexist pefectly at very low pH.

3. This can easily be explained. The blue solution contains copper (II) and free ascorbic acid. On addition of excess NaOH, this reacts again to yellow cuprous oxide. The addition of alkali strongly shifts the redox potential for copper (II) to copper (I). This is why at low pH the blue copper (II) remains in solution, while at high pH the copper (II) is reduced by the ascorbate, formed in the alkaline solution.

4. Not easy to explain. The bubbling most likely is due to some acidity, but the black stuff I cannot easily explain. My guess would be that this is very impure copper metal, formed at the zinc metal surface. Zinc may also reduce other stuff in solution and this may give rise to the black stuff.

5. What kind of green color? Is it a bright cyan green color, or a darker moss-green or brown-green color. The cyan compound is basic copper carbonate, if the precipitate is dark green like some moss plants, then it is copper carbonate, mixed with copper (I) compounds. It is remarkable what the combination of copper (I) and copper (II) in a single compound does with its color. It impairs a very dark green/brown color to such compounds.


I also have done quite some experimenting with copper (I) oxide. I found a relation between the speed of formation and the color. Fast formation --> bright yellow, slow formation --> brick red. All colors from bright yellow through several oranges to brick red can be made. See the following two pictures I made of a copper (I) solution and the two extremes of the copper (I) oxides.

Copper (I) solution in dilute ammonia, which is oxidized by oxygen from air, forming the deep blue tetrammine complex.
http://woelen.homescience.net/science/chem/solutions/cuI-2.j...

Yellow Cu2O:
http://woelen.homescience.net/science/chem/solutions/cuIoh.j...

Red Cu2O:
http://woelen.homescience.net/science/chem/solutions/cuIoh-2...

What I found is that making pure copper metal from solutions is not as straightforward as I liked. One process, which gives very fine pure copper metal is preparing such a solution in ammonia, as shown in the first picture and then adding a solution of sodium dithionite. Then pure copper metal is formed. First the liquid becomes blue when viewed through transmitted light and red when viewed with reflected light. Later it becomes turbid and metallic copper settles at the bottom as a very fine brown powder.

Another way is to dissolve copper (II) sulfate or copper (II) chloride in dilute hydrochloric acid and adding sodium sulfite and heating a little. This gives rise to larger crystals of copper metal, but this procedure seems to be somewhat unreliable. I have tried multiple times and not always does it produce copper metal.

<!-- bfesser_edit_tag -->[<a href="u2u.php?action=send&username=bfesser">bfesser</a>: fixed external link(s)]

[Edited on 7/22/13 by bfesser]




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[*] posted on 5-9-2005 at 03:40


2. I’m guessing that one of the byproducts of the initial reaction is some kind of ligand that complexes unreacted Cu<sup>2+</sup> ions, forming that green color. Adding a strong acid causes the free H<sup>+</sup> ions to displace the copper ions from their complex, leaving blue Cu<sup>2+</sup> ions floating around.
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[*] posted on 5-9-2005 at 05:13


1. After looking at your pic wolean, the result is indeed Cu2O.
2. It was 70% HNO3 added to to the green solution
4. I will do more tests later today
5. Olive green

It indeed is copper powder produced as I washed it with 31% HCl without any dissolving. We discussed this a few pages back I believe, and Chemoleo found it conductive as well.




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[*] posted on 29-11-2008 at 07:47
Bright metallic concentrate


I have had some success using the CUSO4 + Ammonia + ascobic acid method to precipetate copper powder. However, the powder ends up looking black. I would like to precipitate a bright metallic powder. Is this possible?
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[*] posted on 29-11-2008 at 17:50


I have very fine lab-grade copper powder. It's BLACK as well!
It actually stains my fingers when I touch it.

Is this even more fine than the red superfine copper powder, you guys are talking about?
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[*] posted on 30-11-2008 at 04:33


Yes I think it is copper, but is so fine so as not to be able to reflect the wavlength of the copper powder. Perhaps the precipitate needs to be produce more slowly...?


[Edited on 30-11-2008 by bluebriant]
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[*] posted on 30-11-2008 at 05:43


An experiment I did years go involved dissolving Mg shavings in ascorbic acid. The resulting substance dissolved completely in water and was much more reactive than just ascorbic acid or Mg shavings. Addition of this solution to a concentrated solution of CuSO4 in water reacted immediately to form a yellow-brown precipitate which then slowly converted into copper precipitate. This copper was exceedingly fine and once dry it got into absolutely everything!



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[*] posted on 30-11-2008 at 06:21


Interesting...Unfortunately I think I need to produce copper in a more cystalline form (rather than amorphous). This will probably need some sort of cyrstalline promotor of sorts, e.g. a sodium silicate matrix?
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[*] posted on 1-12-2008 at 03:36


You'll get metallic crystals from cementation (e.g. powdered zinc). Good old fashioned sintering of the colloidial powder (under hydrogen at maybe >600°C) will of course do something, although it may just stick together as a solid lump. :P

I've got fine copper before, but I can't quite remember why. Maybe it was Cu2O I dissolved in H2SO4 (which disproportionates to CuSO4(aq) and Cu(s)).

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[*] posted on 4-12-2008 at 14:35


That's pretty cool. Nanozized Cu.. Nice. Never even thought of reducing copper(II) salts with ascorbic acid..
(Seems like one often overlooks those conceptually simple but useful reactions for some reason..)
This could be quite useful and seems v. easy if done right and pure ascorbic acid is used..
Luckily I can get it undiluted it at the grocery-store for a few dimes here. :D

Though for those that can't...
Shouldn't Oxalic acid work too? I think it's also more widely available as a pure chemical than ascorbic acid, as it's sold as a rust remover.
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[*] posted on 24-6-2014 at 20:04


I'd really like to revive this thread in order to explore what was in that lovely green solution. Incidentally I made copper powder in this same fashion after hearing about it somewhere else, and now I have loads of the solution left over. Did Davster ever finish his tests? Whether he did or didn't, it would be nice if we at least had an equation relating the reduction of copper sulfate by this method; it's a bit beyond me. I'm quite curious as to where those sulfate ions went.
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[*] posted on 25-6-2014 at 10:34


Dry nano-scale copper powder is easily made from the thermal decomposition of copper oxalate as well. This might prove to be more convenient.

http://eprints.ru.ac.za/9A209DE9-8E5C-4C44-AFD6-ABEBE0F5547D...




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[*] posted on 25-6-2014 at 10:56


Oh yes, the oxalate method is great for metal powders, they're even so fine they're pyrophoric sometimes, as in the case of iron. I'm probably going to make a new thread so that this question of the green leftover solution from the Ascorbic acid method gets some proper attention.
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[*] posted on 5-7-2014 at 14:47


I'm going to hypothesize a formula which seems to be consistent with my observations. Open to correction.

CuSO4*5H20 + C6H8O6 = Cu+ + H2SO4 + C6H6O6 + H2O
copper sulfate + ascorbic acid = copper + sulfuric acid + dehydroascorbic acid + water

(cross-posted here)
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