Sciencemadness Discussion Board - copper acetate and copper powder - electrolysis.

copper acetate and copper powder - electrolysis.

brew - 16-12-2008 at 01:49

I have wanted to make copper(11) acetate, so I thought why not add store bought aprox 5% white vinegar - 500ml, in a single cell, with two copper tubes as electrodes, with around 11V(using just a battery charger here) and around 2 amps running. The vinegar solution within 2-4 hours becomes blue, and after about 12-18 hours I have collected the solution and seperated precipitated copper and have evaporated of the solution thus forming incredibly beautiful deep blue/torquoise crystals - of copper acetate. I haven't got a camera at present as I would like to show the picture. I have checked out a visual of the copper acetate and they look the same. they smell of acetate, I dont think this can be disputed. The mechanism I think, is the hydrogen of the acetic acid goes to the cathode thus gaining an electron and bubbling up, the acetate anions then go to the anode thus forming the metal acetate, this is soluble, hence the copper goes to the cathode, gains an electron and this forms the copper powder precipitate, the anions head back to the anode which then forms the metal acetate again and this repeats. I think this is what is occuring here.

I haven't crunched numbers in this as yet. I haven't worked out the amp hours, and purely checking the pot and pending on the intensity of the solution etc, I either continue or stop,. this I believe is a really simple way of gaining two useful reagants, and able to be done so very easily. My apologies if this has already been discussed. I have quickly looked and noticed a few other methods, but this very much I believe encompasses two useful reagants. It is so OTC. Worthy of including I felt, albeit incredibly simple.

12AX7 - 16-12-2008 at 16:53

Indeed, a successful preparation. Congrats on the beautiful crystals.

Your theory is correct, and indicates exactly why this process is so inconvienient: due to the copper plating out, your efficiency will be somewhere between nearly 100% (if you run so little charge that barely any copper entered solution and therefore none plated out) to nearly 0% (if you run so long that the addition of copper at the anode is exactly balanced by metal plating out at the cathode and the concentration in solution therefore remains constant).

The best method to prepare metal salts such as copper sulfate or chloride is to prepare the oxide, then dissolve in acid and crystallize. The chemistry of this reaction is posted all over (particularly in the "copper salts" thread), have fun.

Tim

brew - 17-12-2008 at 01:33

I didn't mention this in my description, but I'd casualy check every few hours, and wipe the electrode, or swop the leads. Which gave me a middle ground efficiency. And also a supply of copper, in a purified form. I do have copper sulphate, and I could of changed that to its oxide, but initially thought that wouldn't react with the 5% acetic acid, being so weak, but on second thoughts it would. So I will try it. I can make GAA but that is sort of a hasstle . This just seems an easy OTC method for these reagants when perhaps a small amount is necessary, as catalysts from time to time.Plus it is a hasstle free, drama free process, just check in on it every 3 hours etc... I stilll cant get over the crystals, I have never seen anything so spectacular, the color is extraodinary, also knowing that acetates are somewhat delicate, I dried it on a water bath, set on warm, which made the crystals form very nicely. I tend to get a camera soon, and will begin posting such images.

As far as preparing other salts, I check this forum regularly, and look for the best ways all the time. Cheers.

[Edited on 17-12-2008 by brew]

[Edited on 17-12-2008 by brew]

brew - 29-12-2008 at 16:42

Tim,

With that said, I do realise that my thread is somewhat pointless and doesn't promote discussion - or really intersting chemistry. If I could push the rewind button or remove this thread, I would. Perhaps the moderators could do this for me. I just got blown away by the formed crystals and the ease of obtaining two useful chemicals albeit not realising that one can just make these reagants very easily and also without alot of activity and messing around. I also wanted to contribute to a forum, I get so much out of, and it was late in the day, and I got carried away. Before I post again, I will attempt to ensure that what I state is somewhat of interest not only for myself but for others. I will do a good search and make sure I am not covering old ground, or ground that is somewhat pointless. Perhaps if this thread remains, I will discuss future experiments with the copper salts in question.

brew.

adapt method for lead acetate?

UncleJoe1985 - 9-6-2015 at 05:38

Hi everyone, I'd love to adapt this method to make lead acetate - will save from having to buy H₂O₂.

I've tried it at both 3.3V and 12V but get very low yield since within a few minutes, I already see lead starting to plate on the cathode. I'm using a 1.7mm thick lead plate anode (formerly used to shield X ray rooms), a copper cathode, and 5% distilled vinegar. I initially used a titanium cathode but switched to copper after reading that a copper cathode is advantageous by using galvanic corrosion to prevent more reactive metals from plating out.

To me, this is a huge surprise if Brew's experiment was successful. Making copper acetate would face the same problem of copper being plated and to a larger extent than lead.

My qualitative understanding is that initially when the lead ion concentration is 0, only water will be reduced to H₂. Eventually, the Pb concentration will get big enough that plating lead becomes preferred.

I read about using the Nernst equation to calculate the half cell potentials.

actualPotential = E0 - (0.0592 / n) * Log10(productConcentration / reagentConcentration)

Applying this for
2 H⁺ + 2 e- -> H₂ (assuming 5% vinegar has pH 2.4)

0 - (0.0592 / 2)Log(1 / 0.00398^2) = -0.142V

The potential for Pb+2 + 2 e- -> Pb will decrease as the concentration decreases, meaning it becomes harder to do.

I calculate the Pb concentration such that the potential equals -0.142V. This happens at 0.91 moles/L of Pb+2, which is 296g/L of lead acetate, a terrific yield!

For copper, the critical concentration would be 0.0235 moles/L, which is only 4.27 g/L of copper acetate before copper would start plating out.

How can it be working for copper but not lead?

papaya - 9-6-2015 at 14:53

Quote: Originally posted by UncleJoe1985

Hi everyone, I'd love to adapt this method to make lead acetate - will save from having to buy H₂O₂.

I've tried it at both 3.3V and 12V but get very low yield since within a few minutes, I already see lead starting to plate on the cathode. I'm using a 1.7mm thick lead plate anode (formerly used to shield X ray rooms), a copper cathode, and 5% distilled vinegar. I initially used a titanium cathode but switched to copper after reading that a copper cathode is advantageous by using galvanic corrosion to prevent more reactive metals from plating out.

To me, this is a huge surprise if Brew's experiment was successful. Making copper acetate would face the same problem of copper being plated and to a larger extent than lead.

My qualitative understanding is that initially when the lead ion concentration is 0, only water will be reduced to H₂. Eventually, the Pb concentration will get big enough that plating lead becomes preferred.

I read about using the Nernst equation to calculate the half cell potentials.

actualPotential = E0 - (0.0592 / n) * Log10(productConcentration / reagentConcentration)

Applying this for
2 H⁺ + 2 e- -> H₂ (assuming 5% vinegar has pH 2.4)

0 - (0.0592 / 2)Log(1 / 0.00398^2) = -0.142V

The potential for Pb+2 + 2 e- -> Pb will decrease as the concentration decreases, meaning it becomes harder to do.

I calculate the Pb concentration such that the potential equals -0.142V. This happens at 0.91 moles/L of Pb+2, which is 296g/L of lead acetate, a terrific yield!

For copper, the critical concentration would be 0.0235 moles/L, which is only 4.27 g/L of copper acetate before copper would start plating out.

How can it be working for copper but not lead?

For the lead not plate out at the cathode you could (only probably) try to use cathode made out of more electropositive metal, say copper, however I'm not really sure. Also, lead is supposed to dissolve in acids without any oxidant, but the process may be too slow. I can suggest here to try electrolysis of acetic acid with both electrodes made of lead only using AC current instead of DC - the metal is supposed to turn into fine suspension, which will dissolve on it's own much quicker.
Only theoretically, but if you try please report results!

UncleJoe1985 - 10-6-2015 at 07:23

I forgot about overpotentials. So much for being a bookie and using the Nernst equation.

According to chapter 8, Electrodeposition of Lead and Lead Alloys, Modern Electroplating, lead has a high overpotential for hydrogen evolution.

I think what I'm seeing is an avalanche effect. All it takes is for a tiny bit of lead to plate out, which will locally inhibit hydrogen evolution and serve as a beachhead for additional lead plating, which soon covers the entire cathode! At that point, no hydrogen is produced at all due to lead's high overpotential for hydrogen evolution.

Quote:

using AC current instead of DC

I think you're onto something. Normally AC electrolysis would be dumb, but here, it seems it might prevent the lead snow ball/avalanche effect

I'd like to try it, but don't have a low voltage AC source. I guess I can build a simple circuit that has a microcontroller generate a square wave which will be connected to an H-bridge to toggle the polarity of a DC source.

Quote:

the metal is supposed to turn into fine suspension

So you've seen this done before? Reference?

papaya - 10-6-2015 at 12:54

Quote: Originally posted by UncleJoe1985

Quote:

the metal is supposed to turn into fine suspension

So you've seen this done before? Reference?

Lazy to search for them , however there's a quite reputable ukrainian chemistry portal
http://chemistry-chemists.com/N3_2015/ChemistryAndChemists_3...
One of the members posted an article on dissolution of copper into HCL solution using AC current, try to translate it, same may work for Pb/acetic acid.

Quote:

I think you're onto something. Normally AC electrolysis would be dumb, but here, it seems it might prevent the lead snow ball/avalanche effect

No need to complicate, use transformer or variac, or go potentially more dangerous way - connect your cell to the mains in series with AC capacitor (at 50Hz 1uF is approximated to about 3 kOms of resistance, so calculate maximum current from here and voltafe), but this is dangerous if you don't know what you are doing.
Good luck!