why anhydrous copper sulfate is white in colour?

Answer 1

anhydrous copper sulphate is white in colour because it forms an ionic bond with the sulphate ions using the 4s shell electron.when water molecules form bond with copper sulphate as water has two free electron pairs and due to splitting in energy levels of copper atom these electons absorb white light and go to higher energy level and come back to lower level but higher than the initial one and emit blue colour photons.this means that hydrated copper sulphate is blue in colour and anhydrous one due to absence of water molecules is white in colour.

Answer 2

Anhydrous Copper Sulphate

Answer 3

" these electons absorb white light and go to higher energy level and come back to lower level but higher than the initial one and emit blue colour photons " - posted by Jotsaroop


This is the stupidest explanation i've ever heard. There is NO such thing as white photons, and chemical compounds which would absorb ALL photons in the visible range appear black, and there is no fluorescence involved in the colour of copper sulphate, regardless of hydration. And Copper sulphate does not emit any photons in visible range, it only emits infrared photons because of thermal excitations.

The correct explanation:
is that anhydrous CuSO4 has very little covalent character becuse the sulphate ions are very very weak field ligands, the bond lenghts in the solid crystal phase under x-ray diffraction are quite long (~2.4-2.5 angstroms), which is on the brink of an acceptable bond lenght. The energy level splitting in the Cu2+ ions is very small if even measurable, meaning the Cu2+ ion is basically equivalent to a free Cu2+ ion, which does not absorb in the visible range, because the d orbitals are all degenerate.
So all photons go through the crystal or are reflected, (none of the white light is being absorbed) therefore you see white light because white light is composed of ALL colours in equal proportions.

Hydrated CuSO4*5H2O is made up of [Cu(H2O)4]2+ square planar complex cations, the water is covalently bound to the Cu2+ ion with bond lenghts around ~1.9 angstroms and water is a medium-field ligand which splits the d orbitals into 4 energy bands (eg, a1g, b2g, b1g).
The eg, a1g and b2g orbital bands are closely spaced together and one of them (the b1g orbital) is energetically much higher up, this orbital has only 1 electron so you can have some electronic tranzitions from the lower bands to this one. The largest energy gap between these orbitals corresponds to orange light. So all electronic tranzitions will be around that value of orange light, at around ~600 nanometers.

Since this complex now absorbs orange light, it will appear blue to your eyes.

Answer 4

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Cu2SO4 is white goes blue when hydrated.

Answer 5

It absorbs all other photons except white photons

Answer 6

Was asking myself the same thing