Question

When `"copper sulfate pentahydrate"` is heated, a colour change is observed. Why?

Answer 1

Well, this is an example of chemical change, so of course a colour change is expected.....

Explanation:

We gots....`underbrace(CuSO_4*5H_2O(s))_"lovely blue crystals" + Delta rarr underbrace(CuSO_4(s))_"white salt" + 5H_2O(l)`

In the hydrate, the copper is coordinated to water molecules....the water molecules leave the metal coordination sphere upon drying...

The watchglass on the right as we face it, contains anhydrous `CuSO_4(s)`...the colour change is beautiful, and dramatic.

The addition of water ligands modifies the electronic structure of the copper atom....