Sciencemadness Discussion Board

Sodium metal from alternate salts?

White Yeti - 1-1-2012 at 18:57

Sodium metal is usually made by electrolysing a molten mass of sodium hydroxide.

Obviously, sodium hydroxide is a notorious base that can not only fatally injure an experimenter when improperly handled, but can also destroy glass when molten. As an added bonus, partially hydrated sodium hydroxide will not melt properly and can throw bits of molten base at unsuspecting victims.

Hypothetically, can other low melting point sodium salts (like sodium acetate) be used to make sodium metal by electrolysis?

My reasoning is that as long as the salt does not decompose (won't happen if the temperature does not climb too high) anhydrous sodium acetate should work as well as sodium hydroxide for this electrolysis.

Still, a few questions remain. What happens at the anode? What does the acetate anion become when it loses an electron?Does it turn to carbon dioxide and water?

This seems like a much safer alternative to sodium hydroxide, but I fear there must be a catch somewhere.

symboom - 1-1-2012 at 23:01

im with you on that i dont know either of course you mean of sodium acetate (anhydrous)
melting point 324 °C
but this salt does decompose 881.4 °C

Chemistry Alchemist - 1-1-2012 at 23:41

You could always do it via reduction of Sodium Hydroxide with Lithium or Magnesium... but then your left with a reactive metal and maybe a non reactive or hard to get rid off salt...

Endimion17 - 2-1-2012 at 05:17

Sodium is usually not made by electrolyzing sodium hydroxide. Sodium chloride is used. Reduction from the hydroxide is a very old process that fell out of favor fairly quickly when the Downs cell was brought up.

It could be made from other sodium halogenides. Their melting points aren't very low, but appropriate calcium halogenides would lower the melting point of the mixture. I guess it would be easier to obtain it from sodium bromide (larger ion, less energy, blah blah blah). It's just not used commercially because when you sum up all the expenses, electrolyzing table salt is far more cheaper as it's extremely abundant.


If all was neat, acetate should turn to ethane and carbon dioxide, but it's a quite messy reaction, producing lots of crap. The melting point is low, implying that it probably would have been used at some point through the history, but AFAIK that wasn't the case, ever.

[Edited on 2-1-2012 by Endimion17]

neptunium - 2-1-2012 at 06:07

i guess it all come down to how clean and pure you want sodium metal ? reduction with Mg or Li works well but leave a mess hard to seperate from sodium ( although not impossible..)
electrolysis give great purity but the yield is poor ( for a home chemist) and is such a pain to set up and keep going...

you know you can always buy it (gallium source, mettallium, etc... its not expansive and shipps readilly (kinda..)

blogfast25 - 2-1-2012 at 06:48

The NaCl - CaCl2 eutectic is about 600 C MP, still much higher than the MP of NaOH (318 C I believe). If you're only looking to make small amounts of sodium, electrolysing lye is easier at the hobby level. It's not difficult to protect onself against the molten alkali: use a decent glass screen between you and the cell for instance. I've seen this done at class room level w/o any real problems. The molten Na was scooped off using a gauze wire 'spoon' and dumped in paraffinic oil. Blowing argon over the surface will even protect the metal somewhat.

Eutectic finder (database):

http://ras.material.tohoku.ac.jp/~molten/molten_eut_query1.p...

... but it's not loading right now,

[Edited on 2-1-2012 by blogfast25]

symboom - 6-1-2012 at 10:19

Quote: Originally posted by Endimion17  
Sodium is usually not made by electrolyzing sodium hydroxide. Sodium chloride is used. Reduction from the hydroxide is a very old process that fell out of favor fairly quickly when the Downs cell was brought up.

It could be made from other sodium halogenides. Their melting points aren't very low, but appropriate calcium halogenides would lower the melting point of the mixture. I guess it would be easier to obtain it from sodium bromide (larger ion, less energy, blah blah blah). It's just not used commercially because when you sum up all the expenses, electrolyzing table salt is far more cheaper as it's extremely abundant.


If all was neat, acetate should turn to ethane and carbon dioxide, but it's a quite messy reaction, producing lots of crap. The melting point is low, implying that it probably would have been used at some point through the history, but AFAIK that wasn't the case, ever.

[Edited on 2-1-2012 by Endimion17]



but the temps are easier to get to and you have to deal with HOT chlorine gas and sodium has to be under argon tanks aren't cheap

Adas - 7-1-2012 at 02:23

You can still use Nitrogen instead of Argon. And you can heat it up with induction heater.

Fantasma4500 - 11-1-2013 at 14:31

very interesting thread.. i had this as an idea longer time ago, where i went through different alkali metals melting points..
the examble i came to in the book i got the idea from was a picture of industrial production using NaCl which was written as having a melting point og 800*C (or the accurate number) nothing was mentioned about flux like additives, but thats an interesting idea aswell..

my idea was to use a nitrate, as i just dont see much fit in how the reaction between Na and NaNO3 could be??
a user on youtube disconfirmed this idea as the NO3 would react violently with the Na metal..
but NaOH could be done.. and even sodium acetate ive been thinking about with something else...
i saw that when you decompose calcium acetate into acetone and calcium oxide (or calcium carbonate) theres a brief amount of time where the mass is completely molten!
abit off topic i know, but if carbon could be at this time be added, you would have a molten mass that wouldnt have anything attached to it, and it would straight away (or by my idea) it should straight away react with the carbon forming calcium carbide, CaC2..

NaOH would be a great idea as steel usually is nearly resistant to its corrosing properties..

also another thing... lithium azide, wouldnt that be a possibility if using this for making lead / silver azides?

bbartlog - 11-1-2013 at 15:03

I would expect elemental Na to react with the acetate ions somehow, especially at those temperatures. Not that a clean reduction to anything in particular is likely but the oxygen in CH3COO- seems like it would end up reacting with the sodium, leaving you with maybe Na2O and ethoxides or just gunk.

AJKOER - 12-1-2013 at 07:25

Quote: Originally posted by bbartlog  
I would expect elemental Na to react with the acetate ions somehow, especially at those temperatures. Not that a clean reduction to anything in particular is likely but the oxygen in CH3COO- seems like it would end up reacting with the sodium, leaving you with maybe Na2O and ethoxides or just gunk.


I suspect this comment is largely correct. For example, when Sodium oxalate is heated (see http://www.ncbi.nlm.nih.gov/pubmed/18962335 ), one of the products is reported to be Na2CO3. Now, for many less reactive oxalate salts, usually the elemental metal itself and/or the metal oxide is formed (for example with Pb). As such, I would write the reaction sequence as:

Na2C2O4 --Heat--> Na2O + CO2 + CO --> Na2CO3 + CO

and would expect some similarity with sodium acetate.

[EDIT] Came across a reference on the thermal decomposition of various acetates including sodium which may render some insights on the products of electrolysis. To quote:

"Judd and co-workers have investigated the thermal decomposition of the
acetates of sodium, calcium, copper(II) and silver(I) using thermogravimetry
(TG) and differential thermal analysis (DTA), together with analysis of the
gaseous products formed during the decomposition process 27 . Their results
suggest that the major organic product formed is either acetone or acetic acid
depending on whether the final solid product is the metal oxide or pure metal.
In the case of calcium, sodium and copper acetate, thermal decomposition
yields the metal oxide, the former two proceeding via the formation of a metal
carbonate intermediate. "

Source, see page 27 at: https://docs.google.com/viewer?a=v&q=cache:cv5a2PWTzlIJ:...


[Edited on 12-1-2013 by AJKOER]

12AX7 - 12-1-2013 at 07:57

For Na2O to remain, you'd need to eliminate...

2 H3CCOONa = Na2O + (C4H6O3)

And for Na2CO3,

2 H3CCOONa = Na2CO3 + (C3H6O)

(C4H6O3) could be anything from methane to ethanal, smaller units (methanol, methanal) and CO likely being dominant. Since Na2O is a strong base, some of these will certainly react, ranging from alkoxides (as mentioned) to further decomposition products (Na2CO3 is very likely).

Since the CO2 stuck behind as carbonate is fully oxidized, (C3H6O) is richer, little CO being available, more alkanes will be produced. For example, decarboxylation results in methyl radicals which hook up to make ethane.

White Yeti - 12-1-2013 at 09:12

Yep, I wanted to say it myself, but the reaction to sodium carbonate and to some sort of alkane is a more accurate than reaction to sodium oxide and carbon monoxide, carbon dioxide and water. Ethylene would be the dominant by-product, before it reacts with oxygen and burns, in which case, carbon monoxide and dioxide would be produced.

Polverone - 12-1-2013 at 15:39

The only compound apart from sodium hydroxide or halide that I know to work is sodium cyanide. Disadvantages are expense and toxicity (though toxicity is not bad if you keep it away from acids and use reasonable precautions). Advantages are lower working temperature than halides, less temperature sensitivity and product loss through back-reactions than with hydroxide. The cyanide works for potassium formation too, while direct electrolytic formation of potassium from halide or hydroxide is impractical.

SM2 - 16-1-2013 at 10:16

I have heard so don't quote me, that sodium can easily be made by heating the iodide. And, of course, very pure sodium can be had through the very poisonous azide. There are a multitude of salts which can be mixed with salt in small amounts, and which will drastically reduce the M.P.