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Amos
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[*] posted on 29-6-2014 at 05:13
Reaction between copper sulfate and ascorbic acid


A useful method for the precipitation of very fine copper particles involves adding ascorbic acid to a solution of copper(II) sulfate and subsequently boiling. The byproduct of the reaction is a dark emerald-green solution. Can anyone shed some light on what this solution contains, or what the chemical equation for this reaction may be? Analysis of the solution has led me to believe that most of the leftover copper is in the form of monovalent ions, as the addition of sodium hydroxide produces a bright yellow precipitate of hydrous copper(I) oxide.



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[*] posted on 29-6-2014 at 11:22


See here:

http://woelen.homescience.net/science/chem/exps/cu-redox/ind...

There's a yellow solution in the end - could you possibly be seeing a blend of both this odd redox product and some excess copper(II)?




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[*] posted on 29-6-2014 at 15:08


I think that's exactly what I'm seeing, thanks for the link. Now if we could only figure out what that pesky yellow solution is...



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[*] posted on 5-7-2014 at 14:46


Quote: Originally posted by No Tears Only Dreams Now  
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. (link)


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

It's not a complete reaction, of course, so there is CuSO4 & C6H8O6 still in the mix.

C6H6O6 is usual product of using C6H8O6 as a reducer.

The solution doesn't have the "rotten eggs" smell we should expect from Hydrogen Sulphate (HSO4). I didn't see any gas think produced, so any reaction which produces H2 or O2 seems less likely.
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Amos
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[*] posted on 5-7-2014 at 19:26


Thanks for your input opendna. After looking through some literature(and it is sparse) This was a conclusion I came to, but I thought, surely sulfuric acid couldn't form this way, not from some wimpy ascorbic acid, but I don't have the chemistry knowledge to tell you no, either. Dehydroascorbic acid, from what I've read online is merely white or slightly beige in color; where could this yellow be coming from?



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[*] posted on 5-7-2014 at 19:50


http://www.sciencemadness.org/talk/viewthread.php?tid=2654
Talks a bit about this in the third post down. I don't know If it's helpful to you.




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[*] posted on 6-7-2014 at 10:14


Quote: Originally posted by opendna  
[...]
The solution doesn't have the "rotten eggs" smell we should expect from Hydrogen Sulphate (HSO4). [...]
Hydrogen sulfate ion does not produce any rotten egg smell. If that would be the case, then sulphuric acid would have a strong rotten egg smell. Rotten egg smell is from hydrogen sulfide, not hydrogensulfate ion.

Also keep in mind that HSO4 is not an existing entity. What does exist is HSO4(-), an ion, formed from sulphuric acid by splitting off H(+). A simplified reaction equation which quite well describes what happens is the following:

H2SO4 + H2O <---> H3O(+) + HSO4(-)




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[*] posted on 6-7-2014 at 18:01


Quote: Originally posted by The Volatile Chemist  
http://www.sciencemadness.org/talk/viewthread.php?tid=2654
Talks a bit about this in the third post down. I don't know If it's helpful to you.


I had actually seen that, I stumbled upon it while looking for answers, but thanks.




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[*] posted on 14-8-2017 at 11:20


Quote: Originally posted by opendna  
Quote: Originally posted by No Tears Only Dreams Now  
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. (link)


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

It's not a complete reaction, of course, so there is CuSO4 & C6H8O6 still in the mix.

C6H6O6 is usual product of using C6H8O6 as a reducer.

The solution doesn't have the "rotten eggs" smell we should expect from Hydrogen Sulphate (HSO4). I didn't see any gas think produced, so any reaction which produces H2 or O2 seems less likely.


Cu(+) is not copper metal. It is copper in the 1+ oxidation state. The bisulfate ion(HSO4) does not have a rotten egg smell; H2S does.


I still would like to know the reaction behind this, however.




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[*] posted on 1-7-2022 at 15:54


Quote: Originally posted by Amos  
Can anyone shed some light on what this solution contains, or what the chemical equation for this reaction may be?

i just found this paper while trying to increase my yields. The copper is great for making conductive ink.

On page 3 of the attached pdf, labeled pg 68

Quote:

The sample's infrared spectrum presented in Fig. 3 shows the

vibrational modes associated with the presence of the poly￾hydrated ascorbic acid molecules. The peaks of the infrared spec￾trum and their corresponding interpretations are detailed in
Table 1. An L-ascorbic acid molecule contains two hydroxyl (OH)
groups attached to double bonded carbon atoms. nfrared spectrum
of the synthesized particle, however, does not show vibration
modes associated with the C¼C bond. The ascorbic acid may be
oxidized into dehydroascorbic acid. Dehydroascorbic acids in the
aqueous solution may have undergone hydration, thus forming
polyhydrated ascorbic acid molecules. The broad peak at 3198 cm1
associated with O-H stretching modes found in the intermolecular
bonded alcohol groups suggests the formation of networks of the
ascorbic acid molecules.
The infrared spectrum in Fig. 3 also shows unidentified peaks in
the range from 2569 to 1980 cm1
. These peaks are attributed to a
possible bond or a complex formed between the Cu atoms and the
polyhydrated ascorbic acid molecules. The ascorbic acid did not
merely coat the copper metal. Otherwise, it would have dissolved in
water. Instead, it formed a complex, which capped the molecules.
This capping may be only a few molecules thick and is too thin to be
visible in the electron micrographs

If i could trouble someone to translate this into dumbass for me i would be most grateful.

Attachment: 1-s2.0-S2468217918302181-main.pdf (1022kB)
This file has been downloaded 228 times




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[*] posted on 1-8-2022 at 07:18


Quote: Originally posted by Velzee  
Quote: Originally posted by opendna  
Quote: Originally posted by No Tears Only Dreams Now  
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. (link)


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
....


Per above and Wikipedia on Cuprous sulfate (https://en.wikipedia.org/wiki/Copper(I)_sulfate), to quote:

"It [Cuprous sulfate] disproportionates upon contact with water:[4]

Cu2SO4 + 4 H2O -> Cu + [Cu(H2O)4]SO4

It can also be produced by the reaction of copper(II) sulfate and a reducing agent such as sodium thiosulfate. "

So simply, cupric is reduced here to cuprous by ascorbic acid, a reducing agent, creating the unstable cuprous sulfate that breaks down on hydrolysis liberating copper metal.

More precisely on the mechanic of the chemistry of ascorbic acid (see https://en.wikipedia.org/wiki/Chemistry_of_ascorbic_acid ), to quote:

"oxidized with loss of one electron to form a radical cation and then with loss of a second electron to form dehydroascorbic acid...Ascorbic acid is special because it can transfer a single electron, owing to the resonance-stabilized nature of its own radical ion, called semidehydroascorbate."

My depiction:

C6H7O- (aq) -> e- + H• + C6H6O• -> 2 e- + H• + H+ + C6H5O•

As: H• <-> H+ + e−

H+ + e- + C6H5O• -> C6H6O

leaving, at least, an electron for donation, in this case with cupric:

Cu++ + e- -> Cu+

[Edited on 1-8-2022 by AJKOER]
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[*] posted on 9-8-2022 at 04:25


For those interested, accidentally came across this 2015 work here https://pdf.sciencedirectassets.com/271163/1-s2.0-S030881461...

Reference: "Oxygen Dependency of One-Electron Reactions Generating Ascorbate Radicals and Hydrogen Peroxide from Ascorbic Acid" by William L. Boatright.

From Page 16, Equation (1):

AscH– + Cu2+ -> .Asc– + Cu+ + H+ (1)

which, upon further examination, does technically differ from the my proposed 1st reaction step.

More like:

AscH– (aq) -(Transition Metal Presence)-> .Asc– (aq) + e- (aq) + H+ (aq)

[Edited on 9-8-2022 by AJKOER]
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