What happens when you electrolyse sodium bicarb solution?

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Nathan McCorkle

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Nov 27, 2012, 12:41:49 AM11/27/12
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I'm wondering if carbonic acid forms at one of the electrodes

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Sebastian S. Cocioba

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Nov 27, 2012, 12:46:52 AM11/27/12
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Seems like usual electrolysis products of H2 and O2 plus Na and bicarb ions.

Sebastian S Cocioba
CEO & Founder
New York Botanics, LLC

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Nathan McCorkle

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Nov 27, 2012, 1:04:15 AM11/27/12
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I'd like to find or get helped through figuring out the half reactions properly, rather than trusting a fuel economy enhancement via electrolysis tolerant web forum
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Dakota

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Nov 27, 2012, 5:52:20 PM11/27/12
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Are you interested in using it for some particular purpose?  I've used it before as an electrolyte to help in de-rusting a chain I needed and it actually worked pretty well. 

Depending on your cathode and anode material, the standard electrolysis products of H2 and O2 will still be the major products, and compete with side reactions (based on electrolyte / electrode materials).  

At the anode (which electrons flow into)  you'll have water being oxidized to form oxygen gas, but you'll also have the free hydrogen ions immediately neutralizing your weak base you added as an electrolyte (bicarbonate)  to carbonic acid, which is unstable, and decomposes to carbon dioxide and water.  So over time (no idea how long), your bicarbonate will slowly dissapear as it turns into water and CO2.  You can apply Le Chatlier's principle here, and as the CO2 bubbles out, it should continue to drive more carbonic acid to decompose into CO2 and water.

2H2O à O2 +4H+ + 4e-


And at the cathode (which electrons flow out of) water will be reduced, to form hydrogen gas.  If you also connect a rusted piece of metal at this point, for example, it will compete for electrons, and so besides hydrogen gas you will get your reduced metal, say, iron.   


H2O + 2e- à H2 + 2OH-


If you add those two half reactions up by crossing out the same species on opposite sides of the arrow, you'll end up with


  2H2O à 2H2 + O2   which is the overall reaction. 



In addition to the bicarbonate being slowly neutralized, the Na+ ions from the sodium bicarbonate will probably grab some of the OH- ions yielding sodium hydroxide, and over time the solution will become more basic.  


But as for other half reactions, there are none for the bicarbonate system because it is not an oxidation/reduction reaction (note the +4 formal charge of carbon in carbon dioxide, bicarbonate, carbonate, and carbonic acid). It's all just an acid/base and decomposition reaction.


I know carbonic acid, carbonate, bicarbonate, and carbon dioxide all exist in some crazy dynamic equilibrium, which is still studied to this day, because I guess the mechanism for carbonic acid decomposition into CO2 and water still isn't fully understood.  (but water greatly increases the decomposition rate - which is why it is so hard to "observe" it in its natural habitat, so to speak)


To be honest electrochemistry isn't my best area, and the more I read about it after you asked this question, the more I realized how crazy even something as seemingly "simple" as electrolysis of water + an electrolyte can be.


There are so many insane things going on down there at the atomic level, ions zipping from one electrode to the other, electrons being stolen and donated everywhere.  Crazy stuff man!


Grab a piece of pH paper and take a few drops of water with a pipette from close to the two electrodes and check them out.  


I think it's because of bicarbonate's crazy equillibriums with CO2, H2O, and H2CO3 that it's used in our body to control blood pH.


Sorry that's the best I can come up with at the moment









Nathan McCorkle

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Nov 27, 2012, 6:18:47 PM11/27/12
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Wow, thanks Dakota!

I was looking for a way to generate a strong acid in-vitro... hmm, back to looking at chems


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Simon Quellen Field

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Nov 27, 2012, 6:37:06 PM11/27/12
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To answer the original question -- no.
Sodium bicarbonate will gradually decompose into sodium carbonate, water, and carbon dioxide.
But this acid-base reaction has nothing to do with the oxidation-reduction reactions happening
at the electrodes.

Nathan wants to generate a strong acid.
This can be done by electrolysis of salt water.
At the cathode (the negative electrode) you get hydrogen gas.
At the anode (the positive electrode) you get chlorine gas.
The oxygen and the sodium stay in solution as sodium hydroxide, a strong base.
The gases can be burned to form hydrogen chloride gas, which dissolves easily in water to form
hydrochloric acid, the strong acid Nathan wants.


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On Tue, Nov 27, 2012 at 2:52 PM, Dakota <dko...@gmail.com> wrote:

Dakota

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Nov 27, 2012, 6:46:39 PM11/27/12
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Making sulfuric acid on the cheap from copper sulfate found as root killer at hardware stores is pretty easy, and also involves simple electrolysis and pretty colors.


There are also a few ways to make HCl, http://www.youtube.com/watch?v=YGjd7xxTuZw&feature=relmfu

and nurdrage has more videos on nitric acid.

You can also get cheap sulfuric acid and hydrochloric acid (although I don't think concentrated) at hardware stores again, used for stone masonry. 


Pieter

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Nov 28, 2012, 5:45:11 AM11/28/12
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I use sodium biocarbonate in my DNA gel electrophoresis buffer (about 0.2%), because HCO3- has good buffer properties. Carbonic acid will form as soon as more H+ comes available. I have not seen any carbonic acid build up at the electrodes...

Tom Randall

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Nov 28, 2012, 9:35:48 AM11/28/12
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HCl is also found at swimming pool stores, for controlling pH in pools, as muriatic acid.

Eugen Leitl

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Nov 28, 2012, 1:13:10 AM11/28/12
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On Tue, Nov 27, 2012 at 06:46:39PM -0500, Dakota wrote:
> Making sulfuric acid on the cheap from copper sulfate found as root killer

Sulfuric acid is probably the cheapest chemical around.
There's no point in synthesizing everything from
scratch, just buy it.

> at hardware stores is pretty easy, and also involves simple electrolysis
> and pretty colors.
>
> http://www.youtube.com/watch?v=5dUSF9Gl0xE
>
> There are also a few ways to make HCl,
> http://www.youtube.com/watch?v=YGjd7xxTuZw&feature=relmfu
>
> and nurdrage has more videos on nitric acid.
>
> You can also get cheap sulfuric acid and hydrochloric acid (although I
> don't think concentrated) at hardware stores again, used for stone masonry.

A local artist/pigment shop sells hundreds of chemicals, and
very cheap, too.

Cathal Garvey

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Nov 29, 2012, 10:51:28 AM11/29/12
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It's not always available: I have yet to find sulphuric acid available
for sale around Ireland, although HCl is available as 10M solution in
hardware stores.

That said, electrolysing etc. to make hard Sulphuric acid might be a
waste of effort if all you need is a strong mineral acid: use HCl
instead. But if it's gotta be sulphuric, it might not be available locally..
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Nov 29, 2012, 1:44:31 PM11/29/12
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You should be able to get battery acid (even in Ireland - smile).

Nathan McCorkle

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Nov 29, 2012, 3:17:33 PM11/29/12
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Well for little backstory I actually wanted to produce this acid in a micro fluidic channel, thinking I'd  get around having another fluid line

Cathal Garvey

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Nov 30, 2012, 10:06:19 AM11/30/12
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Being honest, I haven't looked very hard for sulphuric acid, so you're
probably right! Although, battery supplies generally appear to be pretty
rare these days; even deionised water isn't so common anymore, as most
new batteries are sealed-gel rather than free liquid. Even if you wanted
to replace the battery acid, you couldn't.

Will keep an eye open for it though next time I'm in an auto store.
Would be handy to have a bit in the lab.

Simon Quellen Field

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Nov 30, 2012, 1:32:49 PM11/30/12
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Discharged lead-acid batteries start with one plate covered in lead sulfate.
Charging creates sulfuric acid from the lead sulfate.

As discussed earlier, running a current through copper sulfate also produces sulfuric acid.
By induction, we might assume that many common sulfates could be used in this way to produce the acid. Sodium sulfate and ammonium sulfate are common fertilizers.

Boiling the dilute acid concentrates it.

Nathan may want to look here:


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