Final answer:
Adding water to anhydrous copper sulfate will rehydrate it, changing its color from white to blue-green due to the interaction of water molecules with the copper ions.
Step-by-step explanation:
If the process is reversible, adding water to anhydrous copper sulfate will rehydrate the compound, restoring its blue-green color. The hydration of copper sulfate is associated with a change in the coordination of the copper ions, as water molecules bond to the copper, altering its electron configuration and thus its color. Hydrated copper sulfate, which is blue-green, consists of copper ions surrounded by water molecules. When water is added to anhydrous (white) copper sulfate, the water molecules interact with copper ions, rearranging the d electrons and causing the substance to regain its characteristic color.
This phenomenon is also used in experimental procedures to determine the composition of substances, such as by heating to remove waters of crystallization from the blue crystals, turning them white and allowing to measure the water content. The color change upon hydration or dehydration can thus serve as an indicator of these chemical changes.
Conversely, the reaction can be reversed by removing water, such as through heating, which will drive off the water molecules and return the substance to its anhydrous white form, demonstrating the reversible nature of the hydration process.