The salt of some metal, which occurs in the form of a mineral, was treated with an excess of hydrochloric

The salt of some metal, which occurs in the form of a mineral, was treated with an excess of hydrochloric acid solution, and a gas with the smell of rotten eggs was released. To the resulting solution was added dropwise an excess of alkali solution, while the formation of a white bulk precipitate was observed, which dissolved in the excess of alkali. Write down the chemical formula and name of the unknown substance. Make two molecular reaction equations that were given in the process of studying its properties.

Suitable for this description is zinc sulfide (ZnS), which occurs naturally in the form of minerals sphalerite (α-ZnS) and wurtzite (β-ZnS), differing from each other by the type of crystal lattice.

When zinc sulfide is treated with hydrochloric acid, a gas with the smell of rotten eggs (hydrogen sulfide, H2S) is actually released:

ZnS + 2HCl = ZnCl2 + H2S ↑.

When alkali is added to the resulting solution, a bulky white precipitate (zinc hydroxide, Zn (OH) 2) actually precipitates:

ZnCl2 + 2NaOH = Zn (OH) 2 ↓ + 2NaCl,

which really dissolves in excess alkali:

Zn (OH) 2 + 2NaOH = Na2 [Zn (OH) 4].