The hydrated copper sulphate
CuSO4.5H2O is blue in color. The ligand (water molecules) cause splitting of d – orbitals. We know that, due to this, the process of d – d transition and color transition is facilitated.
Whereas, on the other hand the anhydrous copper sulphate CuSO4
is colourless. In the absence of ligand (water molecules), splitting of d orbitals is not possible. Hence, d – d transition is not possible.
We can understand the above from the following statements.
CuSO4.5H2O is blue in colour because its oxidation state +2, thus it has unpaired electrons in it. So, d –d transition is possible so it exhibits colour where on the other hand the anhydrous copper sulphate complex, d – d transition is not possible that’s why it is colourless.
CuSO4.5H2O
Cu2+:3d94s0
unpaired electron present so it show colour due to d−d transition.