CuSO4.5H2O is blue in colour while CuSO4 is colourless. Why?
In CuSO4.5H2O, water acts as a ligand and causes crystal field splitting. Hence, d-d transition is possible thus CuSO4.5H2O is coloured. In the anhydrous CuSO4 due to the absence of water (ligand), crystal field splitting is not possible and hence, it is colourless.