ueki
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Electrolysis of NaHCO3 solution with copper electrodes
So, long story short, I was trying to make NaOH, by using electrolysis of a NaHCO3 solution with two copper electrodes. I thought it would be like
using Na2CO3 and it would be Na+ goes to cathode, becomes Na(s), reacts with water and becomes NaOH, and then CO3 goes to anode, reacts with copper,
becomes CuCO3, but I only had baking soda, and I figured it would have pretty much the same effect. Anyways, my power supply was 3 rectifiers
connected in paralell, providing a DC current of about 5 amps and 112-14 V (unstable voltage) also, this was enclosed in a small plastic tube of about
2cm in diameter (it was a pill container), so I suppose this would have had a high current density?
Moving on, like I said, I was expecting NaOH (aq) and CuCO3(s), but almost immediately a dark blue solution formed and continued to become darker. The
solution kind of looked like a foggy CuSO4 solution, almost a sky blue. I kept this running for about 10 mins, and when I took out the electrodes, the
anode had a very thin layer of a navy blue solid.
The copper compound is an aqueous solution. I filtered it twice and there was no precipitate.
I thought, maybe it was a mixture of a copper solid with NaOH, so I mixed some with a solution of MgSO4, thinking if it was, maybe a precipitate of
Mg(OH)2 would form, but nothing happened; the solutions just mixed.
So, does anyone have any clue what this blue solution is?
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12AX7
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LOL
I get a big laugh off this, because I did it years ago. I think I even posted here about it (though good luck searching the archives if you want to
see for sure). Isn't the color beautiful?
I'm pretty sure the reason is that copper forms a carbonate complex which is water soluble. I don't know why it isn't observed by putting copper
salts in with a carbonate solution, or if it is and nobody ever cares about it.
To get the copper out, you might be able to boil it, possibly with acid, in order to release the CO2. You'll need just the right amount of acid, else
the copper (which should precipitate as the basic carbonate or oxide) will dissolve and you'll need to add a base to precipitate it (soda?  ).
The MgSO4 should've precipitated MgCO3 (either the carbonate or basic carbonate), I'm amazed it didn't.
To actually make NaOH, you need electrodes which don't interact, or to control their interaction. For instance, you could electrolyse salt (NaCl) in
a divided cell, so that the catholyte grows more and more basic as chloride is transported to the anolyte, where it reacts with the anode, producing
chlorine gas, which passes off, hopefully to a collection system. Graphite would be a typical anode for this purpose. If you use a reactive
material, like iron or copper, it will form the chloride in solution, and instead of chlorine, you will have a solution of that metal in the anolyte.
Unfortunately, the ions will be attracted to the cathode, so this won't succeed for too long.
Tim
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Mr. Wizard
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Could the bicarbonate ion have been reduced at the Cathode to a formate ion? This would give you a soluble blue copper salt. Somebody with more
insight can set me straight, but it looks like one free hydrogen can pull off an -OH as H2O and another fill it's spot giving you a formate. Any
quick tests for formate?
I'll be sorry I posted this in the morning. 
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ueki
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The reason I used copper electrodes is because I don't want to produce chlorine, because I don't have the apparatus necessary to safely contain or
vent it... and I don't want to make copper chloride, because then it would be hard for me to purify the NaOH solution. Also, I don't have acces to
many chemicals; no bases, and my only acid would be white vinegar  Basically, my
only chemicals are NaHCO3, and then if I really want to, I can convert it to NaCO3 by heating, MgSO4, Table salt, rock salt, calcium chloride ice salt
(so its not pure), white vinegar, and copper metal.
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chloric1
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ueki-have no idea where you are located or your age but you may want to explore your surroundings. For instance you have the following sources that
are cheap, not readily suspicious, and don't normally ask for photo ID's for age verification.
They are:
Garden suppliers: Calcium nitrate, Ammonium Sulfate, Urea, Potassium sulfate, possibly potassium nitrate stump remover or sodium nitate(Nitrate of
Soda).
Pottery suppliers: Cobalt, chromium, bismuth,nickel,zinc, tin, maybe lead compounds, and occasionally vanadium.
Hardware Stores: Solvents, Muriatic acid(HCL), sometimes Conc Sulfuric acid or sodium hydroxide for drain cleaners,potassium permanganate for water
filters.
Never hurts to check taxidermi or brewing supplies(age issue) just to see what is out there.
Many things you may find may not be of highest purity so you might have to do that yourself. Also, I would suggest you get a basic laboratory
chemistry proceedure book from 1960 or before. These older volumes will give you the most concise and no nonsense approach to most typical chemical
manipulations.
As a side note, electrolyzing bicarbonate with copper electrodes is how you make synthetic azurite a copper carbonate-hydroxide mineral.
Fellow molecular manipulator
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ueki
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I think it is azurite, because i left it in an open plastic cup since last night and wikipedia says for copper complexes like azurite: "If left
overnight in an open container, the complex decomposes through the formation of small crystals of azurite on the sides of the container, leaving the
carbonate solution once again colorless." and tahts what happened, not completely, but that's what started to happen.
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experimenter_
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When a NaHCO3 solution is heated while copper metal is inside it, a blue solution is formed over time, probably some soluble complex of copper in
NaHCO3. It would be interesting to perform the electrolysis experiment with K2CO3 solution, maybe this soluble complex is not formed with potassium.
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DFliyerz
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As far as I know, the reaction produces sodium hydroxide and mixed copper carbonates until the sodium hydroxide raises the pH of the solution to a
point where the formation of solid sodium cuprate is favored rather than the continued formation of sodium hydroxide and copper carbonates.
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Zandins
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Would it not be more rational to electrolyse NaCl instead of NaCO3, as the reaction is simpler and has less byproducts?
Refer to the Chlor-alkali thread in the Technochemistry section for guidance.
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