Sulfide Ion, S2-
Sulfide is a strong base, so solutions of sulfide in water are basic, due to hydrolysis. Sulfide solutions develop the characteristic rotten-egg odor of H2S as a result of this hydrolysis.
Many sulfide salts are insoluble in acidic or basic solution:
Acidic: PbS, Bi2S3, CuS, CdS, HgS, As2S3, Sb2S3, SnS2
Basic: CoS, FeS, MnS, NiS, ZnS
Those salts that are insoluble in acidic solution are also insoluble in basic solution.
A common test for aqueous sulfide ion involves acidification to form H2S, then exposure to moistened lead acetate paper to form black PbS on the paper:
S2- or H2S can be oxidized to yellow elemental sulfur in a colloidal form with fairly mild oxidizing agents, including nitric acid.
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