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Solubility Of MS Type Sulfide

wallpapers Resource 2020-11-30
(1) Insoluble in water and hydrochloric acid, but soluble in sulfide of concentrated nitric acid. Such sulfides can undergo redox reactions with concentrated nitric acid, and the S2- in the solution is oxidized to S, and the concentration of S2- is greatly reduced, resulting in the dissolution of sulfides. E.g:
3CuS + 8HN03 → 3Cu(NO3)2 + 3S↓+ 2NO↑ + 4H2O
(2) Sulfide soluble only in aqua regia. For smaller sulfides such as HgS, aqua regia must be used to dissolve them. Because aqua regia can not only oxidize S2-, but also combine Hg2+ with Cl- to dissolve sulfide. The response is as follows:
3HgS + 2HNO3 + 12HCl → 3H2[HgCl4] + 3S↓+ 2NO↑+ 4H2O
Since hydrosulfuric acid is a weak acid, the sulfides have varying degrees of hydrolysis. Alkali metal sulfides, such as Na2S, dissolve in water and make the solution alkaline due to hydrolysis. In the industry, the cheap Na2S is often used as an alkali instead of NaOH, so sodium sulfide is commonly called "alkali sulfide". The hydrolysis reaction formula is as follows:
S2- + H2O HS- + OH-

Alkaline earth metal sulfides will also undergo hydrolysis when exposed to water, for example:
2CaS + 2H2O → Ca(HS)2 + Ca(OH)2
Some sulfides of metals with higher oxidation numbers, such as Al2S3, Cr2S3, will be completely hydrolyzed in water:
Al2S3 + 6H2O → 2Al(OH)3↓ + 3H2S↑
Cr2S3 + 6H2O → 2Cr(OH)3↓ + 3H2S↑
Therefore, these metal sulfides do not exist in aqueous solutions. The preparation of these sulfides must use dry methods, such as the direct combination of metal aluminum powder and sulfur powder to form Al2S3.
Soluble sulfide can be used as a reducing agent to make sulfur dyes, depilatory agents, pesticides and tanned leather, and also to make phosphors.

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