# Chemistry Behind Acid Peroxide Method



## cashr23523 (Jan 18, 2011)

If I'm asking questions answered vefore please direct me to the right threads. I'm trying to understand the chemistry behind the AP method. My questions regard step2 & 3 of adding the chlorox and then the SMB.

Does anyonw know which is the correct chemical formula when creating Auric Chloride by adding Chlorx or bleach?

Eq1 2Au + 3NaOCl + 6HCl => 2AuCl3 + 3NaCl + 3H2O
or
Eq2 2Au + 3NaOCl + 8HCl => 2HAuCl4 + 3NaCl + 3H2O

Reason I ask is b/c I see references to both Auric Chlorid AuCl3 and Chloroauric Acid on the forums. 

I assume using the equation above in stoichemetric amounts has to account of the concentration of HCL and NaOCl that is in Chlorox but can anyone tell me where the 1:4 or 1:2 Chlorox to HCL ratio comes from that I see in the videos or other tutorials? Seems like quite a bit of HCL and Chlorox is being used than what might be calculated with stoichometirc amounts. Seems like that would leave the room for a lot of unwanted chlorine fumes to be created.

Do the other ingredients in Chlorox react as well with the HCl? I'm really interested in the chemistry behind all of it to be honest. So if anyone has an idea or can point me to another article many thanks to you.


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## cashr23523 (Jan 18, 2011)

I guess to answer part of my question, the reason for excess HCL is for the next step when adding SMB. Is that correct? So the SO2 is created.

Na2S2O5 + 2HCl → 2NaCl + H2O + 2SO2


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## cashr23523 (Jan 18, 2011)

After further research I found the answers to most of my question. I don't know if this is posted elsewhere but I just wanted to know the exact equations for all the different reactions. Correct me if any of this is wrong. Obviously we do not do each of these reactions seperately.

2HCL + H2O2 -> Cl2 + 2H2O

Chlorine gas bonds with copper when present and apparently bond with gold to make auric chloride in first step if too much H2O2 is added and no copper left to react with.

Cu + 2HCl + H2O2 -> CuCl2 + 2H2O

The reaction above is more of a side reaction I suppose that occurs when seperating the gold foils from the plastic.

2HCl + NaOCL -> Cl2 + NaCl + H2O

Again it's the chlorine gas in the above equation that reacts with the gold to create auric chloride as below.

2Au + 3Cl2 -> 2AuCl3

I suppose this answers my first question of which kind of auric chloride is created or the molecular formula.

Na2S2O5 + H2O -> 2NaHSO3

When adding Sodium Meta Bisulfite to water you get Sodium Bisulfite. 

3NaHSO3 + 2AuCl3 + 3H2O -> 3NaHSO4 + 6HCl + 2Au

Once the sodium bisulfite reacts with the auric chloride the gold is dropped and HCl and Sodium Bisulfate are created.


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## carcrossguy (Jan 18, 2011)

Interesting. Why doesnt all the chlorine gas just escape into the atmosphere? Or is chlorine gas produced slowly and dissolves in the liquid? Thanks.


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## cashr23523 (Jan 18, 2011)

carcrossguy said:


> Interesting. Why doesnt all the chlorine gas just escape into the atmosphere? Or is chlorine gas produced slowly and dissolves in the liquid? Thanks.



Typically the reactions are combined so you wouldn't do each reaction by itself. Most of the time when chlorine is produced it's an intermediate gas and goes back into the reaction to bond with the copper or gold. But thats really why I wanted to know more about it b/c I suppose many of the intermediate gases if the metals are used up will escape as chlorine or some type chloroxide and maybe even sulpher dioxide in the last step. I guess the point is to try and use only the needed amounts or else you pose the risk of making hazardous fumes that could be unhealthy to breath. There is a lot of chemistry going on in these processes. I find that fascinating. I guess the gold is just part of the reward. 8)


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## lazersteve (Jan 18, 2011)

The chemistry behind the Acid Peroxide reaction can be found in the copper chloride etchant document on my website in the documents section.

The reaction of the various etchants and precipitants when dissolving gold is shown here:

Gold Reaction Equations

Steve


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