CHRIS25
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KOH plus S in Water
Hi, I really can not figure this one out for myself. Made liver of sulphur by heating quarter teaspoon of sulphur, melting it in a stainless steel
spoon, when melted I added one flake of Potassium hydroxide, melted that. then put the whole teaspoon in a full glass of warm distilled water.
Ok, but I want to know the chemistry. I have sulphur dioxide gas in the water - that bit I can see from KOH + S + H2O = SO2 + ??? there is obviously
the potassium, where has that gone? I have no clue whatsoever how to balance this equation for my own edification.
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weiming1998
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4KOH(s)+3S(l)===>2K2S(s)+SO2(g)+2H2O(g)
I believe it goes like this.
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barley81
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Dissolving sulfur in sodium hydroxide (I assume potassium hydroxide works similarly) produces a mixture of sodium thiosulfate and sodium polysulfides.
The polysulfide ions are yellow in solution. Solid potassium hydroxide and liquid sulfur may react differently, as the reaction is at higher
temperature and the KOH is not in aqueous solution.
Reaction is probably something like this:
6KOH + (2n+2)S -> 2K<sub>2</sub>S<sub>n</sub> +
K<sub>2</sub>S<sub>2</sub>O<sub>3</sub> + 3H<sub>2</sub>O
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CHRIS25
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ok still learning, I suppose I need to find some good sites that will teach equation balancing. The Liver of sulphur is then Potassium Polysulphide.
Thankyou all of you. Nice of you to show me how to learn. I appreciate this.
[Edited on 9-4-2012 by CHRIS25]
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woelen
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Liver of sulphur is not only potassium polysulfide. It also contains thiosulfate. Barley81's answer is corrent. No SO2 is formed, this gas cannot
coexist with the alkaline OH(-). If any would be formed, it would react at once to sulfite and water.
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CHRIS25
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Ok, thanks. I read that the difference between a sulphate and a sulphide is that a sulphate always has an oxygen molecule or two or more, but a
sulphide is devoid of all oxygen. Same as a chloride and a chlorate, and any other ates and ides that might exist. Please excuse the amateurism
here.
What is the (2n+2) that he has written, never seen that sort of expression before?
[Edited on 9-4-2012 by CHRIS25]
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barley81
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That was just a means to balance the equation. As potassium polysulfide contains varying amounts of sulfur, I used a variable to denote that. The
variable appears in the coefficient for sulfur on the left side in order to balance the equation.
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CHRIS25
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Quote: Originally posted by barley81  | | That was just a means to balance the equation. As potassium polysulfide contains varying amounts of sulfur, I used a variable to denote that. The
variable appears in the coefficient for sulfur on the left side in order to balance the equation. |
Thankyou Barley.
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AJKOER
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If you want only K2S, consider the reaction of potassium permanganate and elemental sulfur:
2 KMnO4 + S → K2S + 2 MnO2 + 2 O2
Store the K2S away from water (perhaps under ether) as per Wiki: "Sulfide is highly basic, consequently K2S completely and irreversibly hydrolyzes in
water according to the following equation:
K2S + H2O → KOH + KSH
For many purposes, this reaction is inconsequential since the mixture of SH− and OH− behaves as a source of S2−. Other alkali metal
sulfides behave similarly.[1] "
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Polverone
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| Quote: Originally posted by AJKOER | If you want only K2S, consider the reaction of potassium permanganate and elemental sulfur:
2 KMnO4 + S → K2S + 2 MnO2 + 2 O2
Store the K2S away from water (perhaps under ether) as per Wiki: "Sulfide is highly basic, consequently K2S completely and irreversibly hydrolyzes in
water according to the following equation:
K2S + H2O → KOH + KSH
For many purposes, this reaction is inconsequential since the mixture of SH− and OH− behaves as a source of S2−. Other alkali metal
sulfides behave similarly.[1] "
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The reaction of potassium permanganate with sulfur is very exothermic, potentially explosive. Potassium sulfide is not plausible as a major product
from this reaction. Just because you can make a chemical equation balance does not mean it reflects laboratory reality. Please take more care to
reference the professional literature or try an experiment yourself before offering potentially dangerous advice.
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AJKOER
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| Quote: Originally posted by Polverone |
The reaction of potassium permanganate with sulfur is very exothermic, potentially explosive. Potassium sulfide is not plausible as a major product
from this reaction. Just because you can make a chemical equation balance does not mean it reflects laboratory reality. Please take more care to
reference the professional literature or try an experiment yourself before offering potentially dangerous advice. |
I am glad we have an oversight on this thread. However, you criticism is entirely misplaced and believe me, I can more than balance an equation, I can
create them.
I suggest you direct your concerns to Wikipedia, as upon further reflection, I am in agreement with your points. As an explanation, please note that
their implicit reference ("Handbook of Preparative Inorganic Chemistry", 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 200)
appears valid.
I, for one, will rethink my blind reliance on their accuracy as they often omit key steps for a successful (safe?) synthesis. Here is the link (I
will not republish their possible rubbish).
http://en.wikipedia.org/wiki/K2S
[Edited on 12-4-2012 by AJKOER]
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Polverone
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| Quote: Originally posted by AJKOER | | Quote: Originally posted by Polverone |
The reaction of potassium permanganate with sulfur is very exothermic, potentially explosive. Potassium sulfide is not plausible as a major product
from this reaction. Just because you can make a chemical equation balance does not mean it reflects laboratory reality. Please take more care to
reference the professional literature or try an experiment yourself before offering potentially dangerous advice. |
I am glad we have an oversight on this thread. However, you criticism is entirely misplaced and believe me, I can more than balance an equation, I can
create them.
I suggest you direct your concerns to Wikipedia, as upon further reflection, I am in agreement with your points. As an explanation, please note that
their implicit reference ("Handbook of Preparative Inorganic Chemistry", 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 200)
appears valid.
I, for one, will rethink my blind reliance on their accuracy as they often omit key steps for a successful (safe?) synthesis. Here is the link (I
will not republish their possible rubbish).
http://en.wikipedia.org/wiki/K2S
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Brauer's Handbook can be found in our own forum library: http://library.sciencemadness.org/library/books/brauer_ocr.p...
The preparation from KMnO4 was not from any handbook, though the Brauer reference was misleadingly placed so it appeared to refer to such.
The Brauer ref on Wikipedia also gave the wrong page number for the synthesis using sulfur and potassium in anhydrous ammonia.
I have edited the Wikipedia page to remove the defective synthesis from permanganate, fix the Brauer page number reference, and add a cited
preparation of potassium sulfide solution from aqueous potassium hydroxide and hydrogen sulfide.
Wikipedia has some good information but it frequently contains flights of fancy in regard to chemical preparations. If you have an excess of spare
time on your hands, you could spend months merely editing Wikipedia chemistry pages to add proper citations and replace fantasy preparations with
documented ones.
Edit: the bunk information was added by an anonymous user just under a year ago, on April 12 2011: https://en.wikipedia.org/w/index.php?title=Potassium_sulfide...
[Edited on 4-12-2012 by Polverone]
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barley81
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Polverone, a user called Smokefoot undid your editing. He says that your method gives KSH, not K<sub>2</sub>S. Considering that the
solubility of hydrogen sulfide is 4g/L, saturating a solution of KOH with it, and then adding another equivalent of KOH, should give mostly potassium
sulfide and only a little bisulfide.
[Edited on 12-4-2012 by barley81]
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AJKOER
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Smokefoot comments are in line with Wiki comments I quoted earlier, which may be the product of more recent research. The cited source is: Holleman,
A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5. To quote:
"Sulfide is highly basic, consequently K2S completely and irreversibly hydrolyzes in water according to the following equation:
K2S + H2O → KOH + KSH
For many purposes, this reaction is inconsequential since the mixture of SH− and OH− behaves as a source of S2−. Other alkali metal
sulfides behave similarly.[1] "
Wiki also notes: "For example, the hydrated form of sodium sulfide, nominally with the formula Na2S · 9 H2O, is better described as NaSH · NaOH · 8
H2O." Link: http://en.wikipedia.org/wiki/Bisulfide
I would speculate that the isolation of Na2S (or K2S) from an aqueous synthesis is problematic at best (although inconsequential as a source of S2-).
I have noticed the reference to the formation of K2S as an important intermediary in Fireworks, which also suggests more recent research. As such,
their cited reaction for K2S may indeed be completely pyrotechnic in nature (a danger of using Wiki as a preparation source) which I should have
caught.
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barley81
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Brauer says that the nonahydrate salt of sodium sulfide (NaSH · NaOH · 8H<sub>2</sub>O) can be dehydrated to very pure
sodium sulfide. Though potassium sulfide is very hygroscopic, perhaps the mixture of hydrated KSH and KOH formed by drying a solution of
"K<sub>2</sub>S" could be dehydrated to K<sub>2</sub>S...
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