Why are sulfides insoluble

Tin II sulfide is insoluble in water and form a yellow brown or dark brown precipitate in water. In qualitative analysis, sulfide precipitating is done in two ways due to solubility of different metal sulfide's are different. Copper II sulfide is insoluble in water and forms a black precipitate.

Also copper I sulfide is insoluble in water. Solubility of CoS is 0. So CoS is insoluble in water but soluble in dilute acids. All alkali metal sulfides are soluble in water. But sodium sulfide is not stable in water and it is hydrolyzed to sodium hydroxide by giving strong alkaline solution. Ksp means solubility product. When Ksp value is low, it indicates that compound has a lower solubility in water.

Lets take several metal sulfides to learn this. You see these metal sulfide's Ksp values are very low and they form precipitates in the water. First of all, I should say, this is an idea. After hydrogen sulfide and other effluent gases are separated in the refining process, it should be sent to aqueous concentrated NaOH solution to produce sodium sulfide.

Then other gases are removed. Produced sodium sulfide is sent into another place and heat the solution. Then sodium sulfide will hydrolysis will emit hydrogen sulfide gas.

You can see, a black color solid is deposited as CoS precipitate in the water. Therefore, CoS is insolble in water. S block metal sulfides - Alkali metals and alkaline earth metals All alkali metals sulfide and alkaline earth metals sulfides are soluble in water and form colourless aqueous solutions. Connect and share knowledge within a single location that is structured and easy to search. For example, silver chloride, silver sulfide, and silver oxide are three exceedingly stable silver salts in water solution.

Does this have to do with charge density of the component ions? This doesn't seem to hold water because we know that silver oxide is much more soluble than silver sulfide, and the oxide anion is obviously a lot smaller than the sulfide ion, so the oxide ion should have a much higher negative charge density. So simple charge density rationalizations go out the window. I've Googled, I've looked in books, etc. Also the sulfide ion should be bigger and has empty 3d valence orbitals which may or may not be accessible to a great extent.

Nonetheless, metals, by nature of possessing a large number of valence d-electrons , may be able to increase the stability of the sulfide ion by populating its d-valence. I also know that silver is a good Lewis acid, as are many metal cations, because of the poor shielding afforded by the d electrons. Also, the silver cation has an empty 5s orbital. Thus, we can form a sulfide-to-cation sigma coordinate covalent bond. We may also form a pi-type coordinate covalent bond as the far-away d-electron density "drifts" to empty 3d valence orbitals on the sulfide anion, making the sulfide anion now more nucleophilic than ever.

Let me know if my rationalizations are incorrect or if there are better explanations of silver salt stability. This is just an unproven guess on my part. Whether compounds are soluble or not depends on 1 how strong the bonding including lattice forces are that hold the compound together e. I don't see anything odd about the ionic radius of the silver ion so I'm guessing that the energy of solvation of the resultant ions would be fairly normal; so it is probably not factor "2" that makes most silver salts insoluble.

Here is a link to an article that suggests that bonding in silver compounds may have a covalent component, it says, for silver salts "the structure has some contribution from covalent bonding. This appears to be bonding the structure together more tightly, as in a giant covalent structure.

If true, this would help explain the insolubility of many silver salts. The extra energy generated through solvation would further assist in solubilizing these silver salts.

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