Oscilllator
National Hazard
Posts: 659
Registered: 8-10-2012
Location: The aqueous layer
Member Is Offline
Mood: No Mood
|
|
Sodium thiosulphate from NaOH and S
In a 500ml beaker was placed 30g of NaOH, which was then dissolved in a minimum of water. 50g of sulfur was then added and stirred with a glass rod.
This was then placed on a hotplate and brought to a boil:
After boiling for about a minute, a vigorous reaction was observed in which most of the sulfur disolved and the remainder of the liquid had a
blood-red colour:
This mixture was then cooled in a water bath, then filtered to obtain a blood-red liquid (a small sample is shown in the picture)
A small portion of this liquid was diluted with water, and a small amount of 30% HCl added. An immediate precipitate of sulfur formed, indicating the
presence of thiosulphate.
The reaction (according to wikipedia) is meant to proceed like this:
6NaOH + 12S = 2Na2S5 + Na2S2O3 + 3H2O
I made sure to add an excess of sulfur, so that all of the NaOH would react, however the product still tests as strongly basic.
I assume that this red stuff in solution is some kind of sulfur polymer manifested from the Na2S5, and the problem is that I cant seem to remove it.
Does anyone have an idea how I could get it to precipitate and so filter it off?
|
|
|
j_sum1
Administrator
Posts: 6218
Registered: 4-10-2014
Location: Unmoved
Member Is Offline
Mood: Organised
|
|
Hey. That's pretty cool.
I think it might be easier to buy sodium thiosulfate, but it is an interesting synth. I might have to try it.
If nothing else, it is good to know that a useful reducing agent like thiosulfate can be made from otc items. And even where NaOH is banned, it is
not impossible to make it.
I concur on the red colour. Some polymeric sulfur thing seems likely. And such things are awkward.
|
|
|
gsd
National Hazard
Posts: 847
Registered: 18-8-2005
Member Is Offline
Mood: No Mood
|
|
It is a mixture of thiosulfate and polysulfide. The red colour is due to latter.
https://en.wikipedia.org/wiki/Sodium_polysulfide
gsd
|
|
|
Daffodile
Hazard to Others
Posts: 167
Registered: 7-3-2016
Location: Highways of Valhalla
Member Is Offline
Mood: Riding eternal
|
|
In Robert Bruce Thompson's illustrated guide for the home chemist, apparently your procedure produces only polysulfide, and the precipitate from the
addition of acid occurs with polysulfide as well as thiosulfate.
|
|
|
chemrox
International Hazard
Posts: 2961
Registered: 18-1-2007
Location: UTM
Member Is Offline
Mood: LaGrangian
|
|
NaOH "banned?" Stupidity of regulators and lawyers never ceases to amaze me. Where is lye illegal? Well in
my state it's considered a 'precursor' which is one of the reasons I got a license.Cool pictures. This reminds me of a college course; Chem 1b,
qualitative analysis.
[Edited on 24-3-2016 by chemrox]
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
|
|
|
Daffodile
Hazard to Others
Posts: 167
Registered: 7-3-2016
Location: Highways of Valhalla
Member Is Offline
Mood: Riding eternal
|
|
Quote: Originally posted by chemrox  | NaOH "banned?" Stupidity of regulators and lawyers never ceases to amaze me. Where is lye illegal? Well in
my state it's considered a 'precursor' which is one of the reasons I got a license.Cool pictures. This reminds me of a college course; Chem 1b,
qualitative analysis.
[Edited on 24-3-2016 by chemrox] |
I don't think its really banned in most places, but more commonly made scarce in its pure form. It gets harder to find in large, pure amounts, a pure
10lb jug I got awhile ago looks like a dream compared to what is available now, the blue and purple pellets filled with dyes and odd crap, in 200g or
less packages.
|
|
|
j_sum1
Administrator
Posts: 6218
Registered: 4-10-2014
Location: Unmoved
Member Is Offline
Mood: Organised
|
|
Well it(NaOH) is not banned round here. But I understand that there are many places where it is not otc.
Much the same as sulfuric acid cannot be purchased easily where I live, but in the US they just pour it down the drain. 
|
|
|
Oscilllator
National Hazard
Posts: 659
Registered: 8-10-2012
Location: The aqueous layer
Member Is Offline
Mood: No Mood
|
|
Yay, somebody brought back my thread!
One thing I have thought about is adding a solvent - is it possible that adding a non-miscible solvent might somehow be able to extract the polymer?
or perhaps drying it out and roasting it might somehow break it up, allowing it to be re-diluted and filtered off.
|
|
|
Zandins
Harmless
Posts: 25
Registered: 18-6-2016
Member Is Offline
Mood: No Mood
|
|
According to wikipedia, sodium sulfite is oxidised by air to form sodium thiosulfate. Perhaps simply bubbling air through the mixture would work?
|
|
|
MrHomeScientist
International Hazard
Posts: 1806
Registered: 24-10-2010
Location: Flerovium
Member Is Offline
Mood: No Mood
|
|
Sodium sulfite and sodium sulfide are very different compounds.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
