CuSO4.5H2O is blue in colour while CuSO4 is colourless. Why?
In CuSO4.5H2O, there are water molecules that act as ligands. These ligands cause crystal field splitting and the d orbitals are no longer degenerate. The electrons can now be excited to a higher d orbital and therefore show colour. Whereas, in CuSO4, there are no water molecules to act as ligands, so no crystal field splitting happens.