When copper sulfate (CuSO₄⋅5H₂O) is heated, it loses its water of crystallization and turns into anhydrous copper sulfate (CuSO₄).

Here's the chemical equation for the reaction:

CuSO₄⋅5H₂O (s) → CuSO₄ (s) + 5H₂O (g)

The anhydrous copper sulfate is a white powder, whereas the hydrated copper sulfate is blue.