Ions which precipitate out of
solution in the
presence of an
acidic solution containing
sulfur are called "Acid insoluble sulfides." When a
compound such as H
2S is placed in an acidic solution, its dissasociation reaction is driven towards the
left because of the excess
amount of H
+ ions in the solution. Therefore, there is little S
2- in the solution. Any ion which still
precipitates out of solution with this
small amount of sulfur ion left, has a very large affinity for the sulfur ion.
Examples of such ions are Cu
2+ and Hg
22+