sceptic
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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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Rainwater
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https://chem.libretexts.org/Bookshelves/Analytical_Chemistry...
I think this will explain it better than i can
[Edited on 29-1-2023 by Rainwater]
"You can't do that" - challenge accepted
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Jome
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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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Cathoderay
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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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sceptic
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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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Mateo_swe
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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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Cathoderay
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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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RU_KLO
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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.
Go SAFE, because stupidity and bad Luck exist.
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