When water is added to anhydrous copper(II) sulfate (CuSO₄), a dramatic color change occurs, and the following reaction takes place:

CuSO₄ (s) + 5H₂O (l) → CuSO₄·5H₂O (s)

Here's a breakdown of what happens:

* Anhydrous copper(II) sulfate (CuSO₄) is a white powder. It lacks any water molecules attached to it.

* Water (H₂O) acts as a reactant, providing the water molecules needed for the reaction.

* Copper(II) sulfate pentahydrate (CuSO₄·5H₂O) is formed. This is a blue crystalline solid. The water molecules are now incorporated into the crystal structure, forming a hydrated compound.

The color change:

The color change from white to blue is due to the formation of the hydrated copper(II) sulfate. The water molecules interact with the copper(II) ions, changing the way they absorb and reflect light. The blue color is a result of this interaction.

Other observations:

* The reaction is exothermic, meaning it releases heat. You might feel the container warm up slightly.

* The reaction is reversible. If you heat the blue copper(II) sulfate pentahydrate, you can drive off the water molecules, reverting it back to the white anhydrous form.

In summary:

Adding water to anhydrous copper(II) sulfate results in a chemical reaction where the water molecules become incorporated into the copper(II) sulfate crystal structure, forming the blue hydrated copper(II) sulfate pentahydrate. This reaction is accompanied by a noticeable color change and a release of heat.