Gypsum compound chemistry question?

Question

for gypsum: (CaSO4·2H2O)

what does the dot between O4 and 2H mean?

Answer 1

That the compound itself is CaSO4, but that in this form, there are two water molecules of crystallization or association with it. I myself use an *. If one fires gypsum to high heat, one gets CaSO4 without any water, which is Plaster of Paris. The person pours the plaster with water into a mold, the CaSO4 sets up with the H2O, and the person has a plaster statue.

Answer 2

dot implies that water molecules are the integral part of the compound structure. Per each CaSO4 unit in the crystal lattice of gypsum there are two water molecules present.