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Topic: Products of a copper + persulfate reaction?  (Read 24131 times)

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Offline DigiTan

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Products of a copper + persulfate reaction?
« on: January 07, 2008, 04:25:52 PM »
I'm currently using an opaque Lewis acid to etch out patterns for copper circuitboards.  I want to retrofit the system to work with a different etchant: most likely a Ammonium persulfate solution.

I'm not 100% sure what the products of that reaction will be.  I know it will produce a copper salt, and I need to know the remaining products so I can dispose of the used solution properly.  Can anyone show me how to balance out a reaction beteen copper and Ammonium persulfate?

Also, in case of a spill, what's a safest way to neutralize the ammonium persulfate?

Offline Alpha-Omega

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Re: Products of a copper + persulfate reaction?
« Reply #1 on: January 07, 2008, 05:57:33 PM »
Copper is  oxidized by persulfate to form soluble
copper sulfate:


Cu + S2O8-2 ——> CuSO4 + SO4-2

and here is the MSDS sheet for copper(II) sulfate:  http://ptcl.chem.ox.ac.uk/~hmc/hsci/chemicals/copper_II_sulfate.html

Data on Ammonium persulfate:
 http://www.fmcchemicals.com/LinkClick.aspx?fileticket=y%2F0DZcxPM4w%3D&tabid=1468&mid=2563

Offline DigiTan

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Re: Products of a copper + persulfate reaction?
« Reply #2 on: January 09, 2008, 02:51:59 PM »
Okay, a few more questions here...

Cu + S2O8-2 ——> CuSO4 + SO4-2

In this notation, I'm guessing the S2O8-2 can represent ammonium persulfate, plus others like Sodium and Potassium sulfates?  Also, where does the ammonium ion fit in on the right hand side of the equation?  

Since these are anhydrous crystals being mixed with water, should I treat the ammonium persulfate as a hydrate?

Also, the brochure on my ammonium persulfate says the solution is non-reusable due to "out gassing."  I'm assuming this is a release of ammonia gas?

Finally, if the solution gets contaminated with a small amount of NaOH, would sodium sulfate be one of the products?
« Last Edit: January 16, 2012, 02:52:07 PM by Arkcon »

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Re: Products of a copper + persulfate reaction?
« Reply #3 on: January 09, 2008, 03:31:48 PM »
To emphasize on what is going on I would put the reaction equation this way:

Cu + S2O82- -> Cu2+ + 2SO42-

Doesn't matter what is counterion for the persulfate, it is just spectator - it doesn't react.

Since these are anhydrous crystals being mixed with water, should I treat the ammonium persulfate as a hydrate?

No... But to be honest I have no idea what do you mean. Please elaborate, I suppose you are misunderstanding something.

Quote
Also, the brochure on my ammonium persulfate says the solution is non-reusable due to "out gassing."  I'm assuming this is a release of ammonia gas?

Ammonia should not evolve here, unless you add strong base. No idea what they mean by "out gassing".

Quote
Finally, if the solution gets contaminated with a small amount of NaOH, would sodium sulfate be one of the products?

Interesting things may start to happen. First of all, copper hydroxide will precipitate. Ammonium cation will react with strong base, yielding ammonia. Ammonia can partially dissolve copper hydroxide... But most likely first stage (precipitation of blue hydroxide, that soon decomposes to black oxide) will dominate. So you will end with black precipitate and dissolved sodium sulfate.
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Offline DigiTan

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Re: Products of a copper + persulfate reaction?
« Reply #4 on: January 11, 2008, 12:16:20 AM »
Okay, I guess you can disregard my question about the hydrate.  I may have had a misconception of what  hydration is.

Ammonia should not evolve here, unless you add strong base. No idea what they mean by "out gassing".
Well, I guess that makes two of us.  All I was able to learn is that the datasheet recommends using the solution within a day of hydrating it.  They say the same of their sodium bisulfate.  My first guess was there was some kind of decomposition at work.  Any other idea of why this solution would go bad in such a short time?

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Re: Products of a copper + persulfate reaction?
« Reply #5 on: January 11, 2008, 03:51:53 AM »
Arghh, decomposition is a key word here. I can't believe I have not realized it earlier :(

2S2O82- + 2H2O -> 4SO42- + O2 + 4H+

It is multistage and goes through Caro's acid and hydrogen peroxide, but in the end solution gets acidified and oxygen evolves, hence degassing.

Sodium bisulfate solution should be stable. Perhaps you mean bisulfite? This one will be oxidized by air oxygen.
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Offline DigiTan

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Re: Products of a copper + persulfate reaction?
« Reply #6 on: January 11, 2008, 06:51:51 PM »
Okay, I guess I have some redox reactions to practice here.  Can you show me all the intermediate steps used to arrive at the final equation?  I'm still trying to get a handle on balancing multistage reactions.

Sodium bisulfate solution should be stable. Perhaps you mean bisulfite? This one will be oxidized by air oxygen.
Whoops, I meant to say "sodium persulfate" on that one.  How can you tell that sodium bisulfate is stable?

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Re: Products of a copper + persulfate reaction?
« Reply #7 on: January 11, 2008, 07:06:09 PM »
S2O82- + H2O -> SO52- + SO42- + 2H+

SO52- + H2O -> SO42- + H2O2

Sulfuric acid and sulfates are stable in general.
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Offline DigiTan

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Re: Products of a copper + persulfate reaction?
« Reply #8 on: January 20, 2008, 07:57:49 PM »
Cu + S2O82- -> Cu2+ + 2SO42-

What is the molecular formula for this going to be?  I'm having trouble learning how to get a molecular equation from the just the ionic equation.  Is it something like...

(NH4)2(S2O8) + Cu <--> Cu(SO4) + (NH4)2(SO4)

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Re: Products of a copper + persulfate reaction?
« Reply #9 on: January 21, 2008, 03:30:46 AM »
Cu + S2O82- -> Cu2+ + 2SO42-

What is the molecular formula for this going to be?  I'm having trouble learning how to get a molecular equation from the just the ionic equation.  Is it something like...

(NH4)2(S2O8) + Cu <--> Cu(SO4) + (NH4)2(SO4)

That's OK, although some parentheses are superficial:

(NH4)2S2O8 + Cu -> CuSO4 + (NH4)2SO4

Note: it is not always simple to came out with molecular reaction, in some cases it may require some stupid tricks. Sometimes it is not worth the hassle.
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Offline DigiTan

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Re: Products of a copper + persulfate reaction?
« Reply #10 on: January 21, 2008, 02:40:02 PM »
How about this Caro's acid?  It kind of seems like it could also react with the copper to get CuSO5.  Can that happen?


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Re: Products of a copper + persulfate reaction?
« Reply #11 on: January 21, 2008, 03:27:06 PM »
Doubtfull in the presence of metallic copper.
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Offline DigiTan

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Re: Products of a copper + persulfate reaction?
« Reply #12 on: January 22, 2008, 04:06:26 AM »
How can you tell for sure?  Does it have something to do with the redox potentials chart?

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Re: Products of a copper + persulfate reaction?
« Reply #13 on: February 26, 2010, 08:55:25 AM »
Checking potential will help but this is strong oxidizing agent in presence of metal that can be oxidized so you will just get more copper sulfate.

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Re: Products of a copper + persulfate reaction?
« Reply #14 on: February 26, 2010, 04:31:00 PM »
That's more or less what I was aiming at.
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