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Author: Subject: Sodium sulphide
nezza
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[*] posted on 10-3-2012 at 12:18
Sodium sulphide


Is there a simple way to make small quantities of sodium sulphide, not via hydrogen sulphide. I can buy kilogram quantities on line but I only need a few grams.
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entropy51
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[*] posted on 10-3-2012 at 13:02


Quote: Originally posted by nezza  
Is there a simple way to make small quantities of sodium sulphide, not via hydrogen sulphide. I can buy kilogram quantities on line but I only need a few grams.
There have been threads on this in the past. The methods that do not use hydrogen sulfide are not simple, they are worse than using H2S for the most part.

You can buy it online from photo suppliers. $5 for 100 grams.

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AJKOER
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[*] posted on 10-3-2012 at 17:54


Here is an interesting path (most likely untried). First, an interesting reaction, heat S and Al (avoid moisture):

2 Al + 3 S --> Al2S3

Depending on how fine the Al, this could be very exothermic (think flash powder).

Add an excess of NaOH and heat again:

6 NaOH + Al2S3 --> 3 Na2S + 2 Al(OH)3

More interesting do it all at once by constructing consecutive layers of Aluminum and Sulfur mix, pure sulfur and then NaOH. Apply heat or ignite.

The reason for the pure S layer is as buffer between Al and the NaOH, which is hygroscopic.



[Edited on 11-3-2012 by AJKOER]
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[*] posted on 11-3-2012 at 23:18


Do you really believe this will give a clean product? NaOH and S also react with each other, without the Al. This combination gives a very complicated mix of sulfide, thiosulfate and polysulfide (the potassium compound made in this way is called liver of sulphur, which is very far away from pure sulfide).

Making pure Al2S3 seems achievable to me, but it will not be easy. Expect a lot of unreacted aluminium and sulphur and also expect polysulfides in the mix. This kind of solid-solid reactions hardly ever give pure products and quantitatively well defined reactions. The main reaction is formation of Al2S3, but there are side reactions.




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AJKOER
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[*] posted on 12-3-2012 at 13:45


Yes, I agree, certainly not a pure synthesis, but an OK excuse to react Al and S and amazingly easier (fun) way than the standard preparation for the anhydrous salt, albeit with an Al2O3 impurity. For example, per Wikipedia:

"Production
Industrially Na2S is produced by reduction of Na2SO4 with carbon, in the form of coal:[3]

Na2SO4 + 4 C → Na2S + 4 CO

In the laboratory, the anhydrous salt can be prepared by reduction of sulfur with sodium in anhydrous ammonia. Alternatively, sulfur can be reduced by sodium in dry THF with a catalytic amount of naphthalene:[4]

2 Na + S → Na2S"

To my prior Aluminum sulfide suggested route, here is a modification: Add strong NH4OH to any of the Al2S3 that may have formed along with any possible un-reacted Sulfur and Aluminum. Filter out (unfortunately, the bad smell of H2S from the Ammonium Sulfide has not been avoided). Expected reaction:

Al2S3 + 2 NH3 + 4 H2O --> (NH4)2S + 2 Al(OH)3

where water is consumed and one can use the flocculation property of Aluminum hydroxide to help clean the solution from particles.

Now add the NaOH (in excess) and mildly heat or, possibly better, add some alcohol in which Na2S is only slightly soluble, to move the reaction to the right. Then, cool to isolate Na2S.xH20, which is the commercially available hydrate. Reaction:

(NH4)2S + 2 NaOH --> Na2S + 2 NH3 (g) + H2O

A source notes the following unwanted reaction:

Na2S + 2 H2O <----> 2 NaOH + H2S

The result, if successful, is hopefully a somewhat cleaner Na2S product in hydrated form.


[Edited on 13-3-2012 by AJKOER]
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nezza
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[*] posted on 15-3-2012 at 02:30


Thanks for the answers. I have found a supplier I can get 100g off so that will do. One more question - How stable is it in aqueous solution ?.
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[*] posted on 15-3-2012 at 04:56


The sulphide anion hydrolizes and forms hydrosulfuric acid which is very weak, so most of the H<sub>2</sub>S molecules exist as hydrogen sulphide which slowly evaporates from the solution. Generally speaking, it takes over 15 minutes for the stench to fully develop after the solid has been dissolved in water.



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[*] posted on 16-3-2012 at 07:37


Quote: Originally posted by Endimion17  
The sulphide anion hydrolizes and forms hydrosulfuric acid which is very weak, so most of the H<sub>2</sub>S molecules exist as hydrogen sulphide which slowly evaporates from the solution. Generally speaking, it takes over 15 minutes for the stench to fully develop after the solid has been dissolved in water.


Per my cited equation:

Na2S + 2 H2O <----> 2 NaOH + H2S

In an open vessel, the formation of H2S gas means that the equilibrium is moving to the right. But, in a closed container with a little added NaOH, the smell should be less noticeable upon opening assuming the vessel is not heated. Also, upon cooling, the formation of the hydrate moving the reaction to the left.


[Edited on 16-3-2012 by AJKOER]
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[*] posted on 23-4-2021 at 04:40


i know thread is old, but heating sulfur with an excess of sodium carbonate gives sodium sulfide and carbon dioxide (if an excess of sulfur, it will react to form polysulfides).
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[*] posted on 23-4-2021 at 06:21


There will be thiosulfate as impurity.



If you are interested in aqueous inorganic chemistry look at https://colourchem.wordpress.com/main-page/

I can offer GC analysis of samples. Just U2U to me for more info.

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[*] posted on 23-4-2021 at 06:50


Heating sulphur with sodium carbonate will give a mixture of sulphide and thiosulphate.

Which is probably still better than heating a mixture of aluminium, sulphur and sodium hydroxide which will give you a shower of molten alkali (with some sulphide, for added toxicity)
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