Heating copper sulfate crystals removes water of crystallization, causing them to turn white. Re-moistening the crystals restores their blue color as water molecules are reabsorbed.
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Heating copper sulfate crystals removes water of crystallization, causing them to turn white. Re-moistening the crystals restores their blue color as water molecules are reabsorbed.
Heating copper sulfate crystals causes them to undergo dehydration, leading to a change in color and composition. Initially, copper sulfate crystals are blue because of water molecules incorporated in their structure. Upon heating, these water molecules are driven off, leaving anhydrous copper sulfate. The color changes from blue to white as the anhydrous form lacks the water-associated color. The composition changes from CuSO₄·5H₂O (copper(II) sulfate pentahydrate) to CuSO₄ (anhydrous copper(II) sulfate). This dehydration is reversible; upon exposure to moisture, the anhydrous form can absorb water molecules, and the blue color is restored as it reverts to the pentahydrate.