Sciencemadness Discussion Board - Sodium Acetate Electrolysis

Sodium Acetate Electrolysis

Chemtastic - 19-6-2004 at 09:38

I have been Googling this one for awhile, and I can't find any hits on it.

The commercial production of sodium is accomplished in a Downs Cell, with fused NaCl (mixed with some other melting point depressor).

This should work with any fused sodium salt, providing that it's stable in the molten state. This being the case, why not use a salt with a lower melting point?

Specifically, why can't I find anything on the electrolysis of molten sodium acetate? It melts at 324 C, little over half the absolute temperature of sodium chloride. It is also readily available, with the mixing of baking soda and vinegar:

NaHCO3(aq) + HC2H3O2 (aq) --> NaC2H3O2(aq) + CO2(g) + H2O(l)

Heat this to dryness, difficult only in the hygroscopic power of sodium acetate. Then collect and melt the crystals. I've checked the MSDS for the stuff, and it doesn't look like anything abnormal. The hydrate is even used in hotpacks (it dehydrates a 130 F -- toasty

).

Anyway, the electrolysis would work like this:

Cathode:

Na+(aq) + e- --> Na(s)

Anode:

2C2H3O2- --> C2H6(g) + 2CO2(g) + 2e-

The anode reaction might be slightly different, but I know that ethane is released.

So...my question stands as to why this is inconvenient to perform. It looks like a perfectly valid source of sodium metal, and it also yields ethane gas, which could probably be used in one way or another...

What disavantages/difficulties are involved in this procedure?

unionised - 19-6-2004 at 10:36

I don't think molten sodium acetate is very stable (I think it will decarboxylate).
I also think that it would react with any sodium that was formed.

Tacho - 19-6-2004 at 13:57

I tried to electrolyse molten sodium acetate. It decomposes badly when molten.

I can't remember exactly what happened, but I remember thinking: "Aha! that's why it can't be used to make sodium!".

Sorry for the spoonfeeding

Chemtastic - 19-6-2004 at 16:29

but what does NaCH3COOH decompose into when it decarboxylizes? Na2CO3? Na2O?

unionised - 21-6-2004 at 14:55

Good question, the "official" decarboxylation (in all the text books)requires the presence of NaOH.
CH3 COONa +NaOH --> NaCO3 +CH3
I guess some combination of this and the decomposition that happens with calcium salts (to give acetone).

Chemtastic - 21-6-2004 at 19:39

Hmmm Interesting...

Darn, I was liking the looks of 324C as a melting point over 804C, but what can you do?

(I assume you meant Na2CO3 and CH4? Pssh, if I wanted those that badly, I'd just turn on the gas stove, and heat some baking soda while I was at it

)

[Edited on 22-6-2004 by Chemtastic]

Tacho - 22-6-2004 at 03:15

The best of using sodium acetate is not the temperature, NaOH also melts at a lower temperature, but molten sodium acetate does not atack glass and the whole thing could be done in common borosilicate glassware!

unionised - 23-6-2004 at 15:06

OOps! two typos in one post, it must hve been a long day.
The best thing about sodium acetate isn't really important if the worst thing is that it doesn't work.

S.C. Wack - 23-6-2004 at 21:02

FWIW, stumbled across a reference today to a Kolbe J. Prakt. Chem. article where he electrolyzed molten potassium acetate.

Apparently he obtained ethane, CO2, ethylene, methyl formate, methyl acetate, methyl carbonate, and H2.

Well...

Chemtastic - 23-6-2004 at 21:15

If only KHCO3 were as easy to come by as NaHCO3...

EDIT:

Or I could just add KOH...der

[Edited on 24-6-2004 by Chemtastic]

xfusion44 - 25-2-2015 at 20:23

Hi, I know that this topic isn't on electrolyzing sodium acetate solution, but I have a question about that...

Would it be possible to make copper acetate by electrolyzing the sodium acetate solution with copper electrodes?

Thanks!

PS: wikipedia says me to use calcium acetate, but I don't have it, so, could I use sodium acetate?

[Edited on 26-2-2015 by xfusion44]

Molecular Manipulations - 25-2-2015 at 20:51

Where would the sodium go? You need a soluble anion. Why not electrolyze acetic acid?
Better yet use anhydrous sodium acetate which is more soluble (over 110 g/100 at 0C), add this to stoichoimetric proportion of a soluble copper salt who's anion is very soluble with sodium in solution.

[Edited on 26-2-2015 by Molecular Manipulations]

xfusion44 - 25-2-2015 at 21:51

So that wouldn't work? I already tried with CH3COOH, but only with 9% vinegar (I don't have glacial acetic acid) and with vinegar it worked VERY slow. So, I was thinking about, how to speed up this and I mixed some NaHCO3 with vinegar (that would give me sodium acetate, which I thought would produce copper acetate with electrolysis, using Cu electrodes). I've already got very dark blue solution after I did this and I was almost 100% sure, that it must have been copper acetate there in solution, but where is the color then from? Wouldn't sodium react with water to give NaOH? What about Calcium (where would it go if I'd use calcium acetate, which is recomended? - wouldn't it make calcium hydroxide?)

What did you mean by using sodium acetate and copper salt? So, that the side product would be NaCl?

Thanks

deltaH - 26-2-2015 at 05:02

According to the wiki article on copper acetate, it can be made by electrolysing a solution of calcium acetate using a copper anode with the accumulation of calcium hydroxide (slaked lime) on the cathode.

The theoretical half reactions are:

Anode: Cu(s) => Cu[2+](aq) + 2e[-]
Cathode: 2H2O(aq) + 2e[-] => H2(g) + 2OH[-](aq)

The reduction of water at the cathode generates hydroxyl anions that precipitates calcium ions as calcium hydroxide (slaked lime) on the cathode.

If you had used sodium acetate and electrolysed with copper, then there is no calcium to precipitate, but the copper cations entering into solution can certainly precipitate under the basic conditions. You would see this as a turquoise-coloured haze. The copper ions could also be reduced at the cathode, but I suspect that would precipitate before they had a chance to reach it because of the pH of sodium acetate solutions, perhaps even forming a copper hydroxide layer on the anode?

[Edited on 26-2-2015 by deltaH]

xfusion44 - 26-2-2015 at 10:48

@deltaH

Thanks for explanation

The color is more dark blue, than turquoise. On the cathode I've got a lot of copper precipitate, but the anode was getting thinner. Bubbles were only forming at the cathode, I think.

Shouldn't I get NaOH? If there would be NaOH, how would I be able to separate it from copper acetate?

Also, could I make copper acetate by electrolyzing solution of NaHCO3 and then react obtained CuCO3 with vinegar to make copper acetate?

Thanks

Molecular Manipulations - 26-2-2015 at 10:49

How does that work? Copper hydroxide is far more insoluble than calcium hydroxide.

Molecular Manipulations - 26-2-2015 at 11:02

Quote: Originally posted by xfusion44

1) Shouldn't I get NaOH? If there would be NaOH, how would I be able to separate it from copper acetate?
2) Also, could I make copper acetate by electrolyzing solution of NaHCO3 and then react obtained CuCO3 with vinegar to make copper acetate?

1) That's why it won't work with sodium acetate. Sodium hydroxide is a very strong base, and will give a hydroxide ion to a copper (II) ion to precipitate copper (II) hydroxide.
2) Well "CuCO₃" doesn't exist, but you might be able to get a hydroxycarbonate to precipitate. I wouldn't do that though, you could use the copper hydroxide from the sodium acetate cell.

xfusion44 - 26-2-2015 at 11:28

Oh, now I understand why it doesn't work. So the solution is blue due to copper hydroxide?

How that it doesn't exist? Here is the wikipedia link: http://simple.m.wikipedia.org/wiki/Copper%28II%29_carbonate

Isn't it possible to make it by mixing CuSO4 + NaHCO3 solution, to precipitate it? Or is it "basic copper carbonate"?

How could I use copper hydroxide? What do I need to do with it, to get acetate? React it with acetic acid? But wouldn't it react immediately when it forms in the cell with remaining acetic acid?

Thanks

Molecular Manipulations - 26-2-2015 at 11:47

The forumula in that Wiki page is simply wrong, I think the formula is Cu₂CO₃(OH₂)₂
Here's the real page
There quite a few threads on this.
Yes you can just add dilute acetic acid to copper hydroxide.

[Edited on 26-2-2015 by Molecular Manipulations]

deltaH - 26-2-2015 at 11:59

Quote: Originally posted by xfusion44

@deltaH

Thanks for explanation

Yes, if you use a saturated sodium bicarbonate electrolyte (washing soda even better), you ought to make a basic copper carbonate precipitate at the anode and sodium hydroxide at the cathode. You should be able to filter and wash the precipitate and it also ought to react with vinegar to make a copper acetate solution. If it bubbles when doing so, it contained a basic copper carbonate. When I speak of basic copper carbonate, I mean mixed hydroxide/carbonate compounds like malachite, Cu2CO3(OH)2, for example.

[Edited on 26-2-2015 by deltaH]

deltaH - 26-2-2015 at 12:08

Quote: Originally posted by Molecular Manipulations

Where would the sodium go? You need a soluble anion. Why not electrolyze acetic acid?
Better yet use anhydrous sodium acetate which is more soluble (over 110 g/100 at 0C), add this to stoichoimetric proportion of a soluble copper salt who's anion is very soluble with sodium in solution.

[Edited on 26-2-2015 by Molecular Manipulations]

Acetic acid is a weak acid, so in solution it only partially ionises, this means that it isn't a great electrolyte. Good electrolytes should ionise fully and so generate a high concentration of ions, hence why soluble salts, strong acids or strong bases are used. One can go one step further and use molten salts or low-temperature ionic liquids as 'super electrolytes'.

[Edited on 26-2-2015 by deltaH]

Molecular Manipulations - 26-2-2015 at 12:12

It will still conduct electricity, just put the electrodes closer and increase the voltage. Yields may not be as good.

xfusion44 - 26-2-2015 at 12:43

Ok, thanks to both of you

So, would be better to:

a)Electrolyze a solution of NaHCO3 and then use copper carbonate with acetic acid to obtain copper acetate

b)React NaHCO3 and CH3COOH and then electrolyze solution to make copper hydroxide and react it with vinegar to make copper acetate

c)Simply electrolyze vinegar with higher voltage

What would you prefer?

Also, if I'd use option a, how would I separate NaOH from copper acetate?

Thanks

blogfast25 - 26-2-2015 at 12:44

Quote: Originally posted by xfusion44

How that it doesn't exist? Here is the wikipedia link: http://simple.m.wikipedia.org/wiki/Copper%28II%29_carbonate

That 'simple.m.wikipedia.org' (huh?) page is complete nonsense.

'CuCO3' DOES NOT exist. Precipitation of copper(II) with a soluble carbonate or bicarbonate ALWAYS yields Cu2CO3(OH)2 ('basic copper carbonate' or 'copper basic carbonate', aka Malachite), never CuCO3.

As regards copper(II) acetate, I'm sure there are plenty of threads on it on this forum. Search?

[Edited on 26-2-2015 by blogfast25]

deltaH - 26-2-2015 at 12:48

Quote: Originally posted by Molecular Manipulations

It will still conduct electricity, just put the electrodes closer and increase the voltage. Yields may not be as good.

A spirit vinegar typically contains about 5% acetic acid, that corresponds to 0.83M, resulting in a concentration of ions of only 0.0076M at equilibrium.

[Edited on 26-2-2015 by deltaH]

xfusion44 - 26-2-2015 at 12:49

@blogfast25

Yeah, I'm on my cell phone and it looks like it's sort of mobile page... Otherwise I get the proper copper carbonate link if I just type "copper carbonate" instead of CuCO3.

Molecular Manipulations - 26-2-2015 at 12:53

It still works, I've tried it. It's very slow, and a lot of current is wasted heating the solution.

Quote: Originally posted by xfusion44

a)Electrolyze a solution of NaHCO3 and then use copper carbonate with acetic acid to obtain copper acetate?
Also, if I'd use option a, how would I separate NaOH from copper acetate?

You won't need to, copper hydroxycarbonate is highly insoluble, just filter it and dry it, you could even decompose it to copper oxide/hydroxide. Then add it to acetic acid solution to make copper acetate.

xfusion44 - 26-2-2015 at 12:56

Quote: Originally posted by Molecular Manipulations

It still works, I've tried it. It's very slow, and a lot of current is wasted heating the solution.

Quote: Originally posted by xfusion44

a)Electrolyze a solution of NaHCO3 and then use copper carbonate with acetic acid to obtain copper acetate?
Also, if I'd use option a, how would I separate NaOH from copper acetate?

Thanks

But would that be the option to go with?

deltaH - 26-2-2015 at 12:59

Quote: Originally posted by xfusion44

Ok, thanks to both of you

Stop using the term copper carbonate or blogfast may go postal

It's called 'basic copper carbonate'.

You won't need to separate the NaOH from the copper acetate. When you filter you basic copper carbonate, you wash it at the filter thereby getting rid of sodium salts. Then when you react the washed precipitate, you should get a reasonably pure solution of copper acetate. Purify further by performing a controlled crystallisation.

Molecular Manipulations - 26-2-2015 at 13:01

zzzzzz...
Oh, what? That again...?
Option A "Electrolyze a solution of NaHCO3 and then use copper carbonate with acetic acid to obtain copper acetate" You could use either sodium carbonate, bicarbonate or hydroxide. The first two will precipitate Malachite the latter copper hydroxide. Add the precipitate to vinegar, Malachite will bubble carbon dioxide, hydroxide will just dissolve.

xfusion44 - 26-2-2015 at 13:07

@deltaH

Would it be better to call it dicopper carbonate dihydroxide?

@Molecular Manipulations

Ok, thanks

I'm sorry for questioning so much, I'm not a pro

deltaH - 26-2-2015 at 13:07

Sodium hydroxide as electrolyte would probably give you the highest possible rates, so if you have lye, use it, as opposed to using carbonates which won't dissolve as well, but in the end, they should all work.

xfusion44 - 26-2-2015 at 13:10

@deltaH

Ok, thanks

xfusion44 - 26-2-2015 at 14:04

Quote: Originally posted by Molecular Manipulations

Quote: Originally posted by xfusion44

I've forgot to mention this:

When you said, that I'd get copper (ii) hydroxide...

Copper hydroxide is almost insoluble in water, so I'd be able to obtain it by filtration, but what I've forgot to mention is, that I didn't add enough baking soda to react with all of the vinegar, so I still had a lot of vinegar in the cell during electrolysis, so I think that it reacted with copper hydroxide immediately when it was created in the solution.

So, I filtered solution and there was no precipitate on filter, probably because of excess vinegar.