What is the effect of heating on the color of CuSO4.5H2O?

Heating copper(II) sulfate pentahydrate (CuSO4·5H2O) leads to the loss of water molecules from its structure. When heated, this hydrated form of copper sulfate undergoes dehydration, resulting in the formation of anhydrous copper(II) sulfate (CuSO4).

As the water of hydration is removed, there is a noticeable color change from blue, characteristic of the hydrated form, to a white or light grey color of the anhydrous form. This transformation occurs because the water molecules are integral to the structure and color of the copper sulfate complex. The absence of these molecules alters the electronic environment of the copper ions, which affects how they interact with light, thus changing the observed color.

This process highlights the importance of hydration in determining the physical properties of certain compounds. The loss of water in this particular case is a direct cause of the color change, making this choice the accurate response to the question posed.