I would like to know the sodium sulfide actual state level in the solution.
Biochemistry, Chemistry, Polymer chemistry, Biophysics
It exists as Na+ and SH-, the sulfide of more basic than the hydroxide so it deprotonates water, so for 1 mole of Na2S in water you get 2 Na+, 1 SH- and 1 OH-
You may fiind useful to see the following (related) discussions: https://www.researchgate.net/post/How_do_you_prepare_sodium_polysulfide_Na2Sx_in_aqueous_solution https://www.researchgate.net/post/Is_there_a_method_available_for_preparing_a_stable_polysulfide_electrolyte_redox_system
A refinement on the answer by Allende: The pKa of H2S is 7, thus if you bring the pH of the alkaline solution to 7 the concentration of HS- equals that of H2S.
Dear Dr Tomás Allende , please do you have a reference for this ? I am wanting to cite this
S2- is not formed upon dissolution of Na2S. Have a look at P. M. May, D. Batka, G. Hefter, E. Königsberger, and D. Rowland. Chem.Commun. 54 (16):1980-1983, 2018, Article Goodbye to S 2– in Aqueous Solution
A species can exist in water as long as it's pKa is between 0 and 14, as long as you adjust the pH. The pKa1 of H2S is about 7, so in neutral conditions hydrogen sulfide and hydrosulfide will both be present. If the pH is higher, then the most abundant species will be hydrosulfide, but the pKa2 is about 17, so it's 3 orders of magnitude higher than the pKb of water, so if S2- is present in water, it will abstract a proton from water since it's a much stronger base. Same reason why hydride, oxide, nitride, phosphide and other highly basic anions cannot exist in water, it's the same reason ammonia as NH3 cannot exist in concentrated sulfuric acid.
In chemistry we tend to use sulfide as a strong soft lewis base. Some people get confused because in a solution of sodium sulfide, silver precipitates as silver sulfide, so they assume the anion must have been present, but this is not a ionic reaction, the sulfur-silver bond is covalent. Because sulfur has a very high affinity to soft acid metal cations (silver, lead, mercury, thalium) and because the sulfides have almost no solubility in water, what really happens is the formation of, in this case silver sulfide, drives an hydrogen out of the hydrosulfide, even if it's not favorable in a purely acid/base point of view.
The simple way of putting it is sulfide is a strong enough base to react with water, so the equilibrium can't favor the existence of sulfide since as long as there is water, the sulfide anion will deprotonate it to form hydrosulfide.
Not the best source but it works.
Article Chemical Foundations of Hydrogen Sulfide Biology
For a somewhat related RG query: https://www.researchgate.net/post/Why_is_Na2S9H2O_black
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