Question

What do we call the salt, `ZnSO_4*7H_2O`?

Answer 1

Zinc sulfate heptahydrate can be isolated as colourless crystals.

Explanation:

`ZnSO_4*7H_2O` can be isolated as colourless, macroscopic crystals. The 7 water molecules are often referred to as waters of crystallization.

Can the water be removed? Yes, but it's a damn inconvenience to do so. Long heating under vacuum would give the anhydrous product as a white powder. There might also be chemical means to dry the salt, such as by prolonged heating to reflux in thionyl chlorde or trimethylsilyl chloride (both of which reagents react with water!).

Zinc sulfate was known as white vitriol historically, because it is the salt of zinc and oil of vitriol (=sulfuric acid; `H_2SO_4`).