Question

The black "smoke" that flows out of deep ocean hydrothermal vents is made of insoluble metal sulfides suspended in seawater. Of the following cations that are present in the water flowing up through these vents, which ones could contribute to the formation of the black smoke?

Pb2+
Mn2+
Mg2+
Cu2+
Na+
Li+
Zn2+
Fe2+
Ca2+

Answer 1

The solubility rules usually go on to say that group IIA sulfides are soluble, but actually group IIA sulfides react with water to make H2S and the group IIA metal hydroxide.