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Author: Subject: Help identifying electrolysis products
sceptic
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[*] posted on 28-1-2023 at 00:30
Help identifying electrolysis products


Recently I electrolysed a saturated solution of sodium bicarbonate with two lead fishing weights as electrodes. I hoped that it would produce hydrogen peroxide, since lead has a high electrode overpotential for the evolution of both hydrogen and oxygen. After running the electrolysis for about 24 hours at 4.0 volts and 0.13 amps, I took a sample of the liquid and added a few small crystals of potassium permanganate to decompose any hydrogen peroxide. I didn't see any reaction. However, the next day I saw that the potassium permanganate solution was reduced to manganese dioxide, so it must have oxidized something.

According to this paper carbon dioxide can be electrochemically reduced on a lead cathode to formate, meaning that my solution might have sodium formate in it. According to wikipedia, carbon dioxide can be electrochemically reduced to formate, carbon monoxide, ethylene, and ethanol.

How can I tell what, if anything, was formed in my solution? I'm assuming that something was, since the potassium permanganate was reduced.
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[*] posted on 28-1-2023 at 17:29


https://chem.libretexts.org/Bookshelves/Analytical_Chemistry...
I think this will explain it better than i can

[Edited on 29-1-2023 by Rainwater]




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[*] posted on 29-1-2023 at 01:11


Titrate the sodium carbonate by itself to see if reductants were present in it from the beginning. Make a reduction standard solution using something like sodium oxalate, then make a KMnO4-solution and standardize the latter by the former.

Now, the critical question is, when you titrate the post-electrolysis solution, is there more reductant than before electrolysis?

IIRC many reactions are easily reversible, so most if any formed formate might be immediately destroyed by the anode.
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[*] posted on 30-1-2023 at 12:02


Those are good suggestions for researching what happened.
I am wondering where you got the idea for producing hydrogen peroxide this way?

Fishing sinkers are probably not pure lead, many might be made from scrap containing tin, antimony or the like.
Many organic substances can decompose hydrogen peroxide, contamination of materials in the cell can spoil things.

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[*] posted on 2-2-2023 at 11:59


Thank you for the helpful replies, I'm sorry I took so long to reply.

I'll try to find a standard oxidizing solution to titrate the solution.

I thought that I might be able to produce hydrogen peroxide this way because numerous methods are known for producing hydrogen peroxide by electrolysis of water. It can seemingly be produced either by reduction or oxidation of water. Lead electrodes have high overpotentials for the evolution of both hydrogen and oxygen, so they seemed more likely to produce alternate products. I should have found another anode material, and used a sulfuric acid solution, but I wanted to be able to use a lead anode without dissolving it, so I thought that a carbonate solution could work as well.

The fishing sinkers might have been a problem, but they were the only source of lead I had available. I think that if hydrogen peroxide had been produced, it would have destroyed any organic contaminants long before the experiment terminated.
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[*] posted on 3-2-2023 at 03:32


If you want hydrogen peroxide you can concentrate the commonly avaliable 3% H2O2 by evaporating the water.
Maybe not an option if you want much of though as it would be expensive.
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[*] posted on 3-2-2023 at 15:54


If you are producing peroxide it probably isn't being very fast.
Some contaminates could be catalyst to decompose the peroxide as fast as it is produced. Catalysts are things (not always compounds) that stimulate a reaction without undergoing any permanent change.
Hydrogen peroxide oxidizes things and is destroyed in the process.
High purity chemicals are classified as "Reagent Grade", a little less pure is "Technical Grade", still less pure is "Commercial Grade". The reagent grade is the most expensive. Professional chemist use reagent grade when they want prove an idea to be sure of what is there and therefore most likely to work according to their expected reaction.
I recommend that you view this YouTube video by Scrap Science to give you an idea of how difficult this process can be. He doesn't get it to work but he gives a link to a paper by someone that found a successful method.
https://www.youtube.com/watch?v=HjO8lv0qJnw
I think someone very recently came up with a method that uses a solid electrolyte.

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[*] posted on 8-2-2023 at 10:37


try searching for electro-Fenton process.

"A typical electro-Fenton process consists of two electrodes in an undivided cell with aqueous Na2SO4 electrolyte at pH 3. The optimal pH for the Fenton method is pH 3
The H2O2 concentrations produced by the electro-Fenton process range from 10 ppm to 2 %.
The most frequently used cathode catalysts are carbon based materials
"
(from a picture I saw O2 is bubbled next to the cathode) maybe a graphite/carbon rod could be used as diffusion rod. Check scrap science video in previous post)

but the problems arises how to remove H2O2 from the Na2SO4 solution.




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