Question

$CuS{O}_{4}5H2O$ is blue in color ?

• A. It contains water of crystallization
• B. $S{O}_4^{-2}$ ions absorb red light
• C. $C{u}^{+2}$ ions absorb red light
• D. $C{u}^{+2}$ ions absorb all color except red from white

Answer 1

Answer: (A)

It contains water of crystallization

Anhydrous $CuS{O}_4$ is white in colour due to the absence of water molecules. When we make the solution of $CuS{O}_4$ water molecules will attach to $CuS{O}_4$molecule making $CuS{O}_4$.Two of the orbitals interact with the water molecules and raise in energy. The energy difference is equivalent of the wavelength of blue light.
The blue colour of the $CuS{O}_4$ is because of Cu(II), which means it had lost two electrons; it gives the copper a 2+ charge.
Due to the arrangement of d-orbitals, there is a splitting effect. There are 5 d orbitals that can interact with other orbitals. Two of the orbitals interact with the water molecules and raise in energy. The energy difference is equivalent of the wavelength of blue light. When the copper absorbs photons, it releases energy from the upper-level energy orbitals back to the lower orbitals, giving blue light.