What is the formula copper sulfate pentahydrate?
Copper sulfate is normally found in the form of blue crystals, copper (II) sulfate pentahydrate. When you heat copper sulfate pentahydrate it turns white as the water which is driven off by the heat. The white solid remaining is anhydrous copper sulfate. If you add water to the anhydrous copper sulfate an exothermic reaction occurs, you can feel the test-tube getting hot, as the blue copper sulfate pentahydrate is re-formed.
The gram formula unit mass of copper (II) sulfate pentahydrate is 249.68. The gram formula unit mass of water is 18.015. Therefore, the mass of water of crystallization present in 50.0 g of copper (II) sulfate pentahydrate is: 50[5(18.015)/249.68] or 18.0 g, to the justified number of significant digits. (Note that the prefix penta- means five)
The difference is that anhydrous copper(II) sulfate has no water of crystallisation. The anhydrous variant is a white solid while the hydrated variant is blue. Also, the chemical formula for hydrated copper(II) sulfate (or copper sulfate pentahydrate) is CuSO4.5H2O while that of the anhydrous one is CuSO4.