Chemistry
Chemistry
Problem
When blue copper(II) sulfate pentahydrate crystals are gently heated, they turn into a white powder that becomes blue again upon the addition of water. Decide whether the heating step represents a physical change or a chemical change and cite one piece of evidence to support your decision.Intuitive explanation
The key is recognizing that heating removes water molecules trapped in the crystal structure—the copper(II) sulfate itself stays chemically intact. Since water can be restored by adding liquid, and the compound never breaks apart or forms new substances, this is a physical change. The color shift from blue to white happens because the hydrated complex (blue) loses its water ligands, revealing the anhydrous salt, but the copper and sulfate ions remain unchanged—they just reorganize their arrangement.
Intuitive explanation
The key is recognizing that heating removes water molecules trapped in the crystal structure—the copper(II) sulfate itself stays chemically intact. Since water can be restored by adding liquid, and the compound never breaks apart or forms new substances, this is a physical change. The color shift from blue to white happens because the hydrated complex (blue) loses its water ligands, revealing the anhydrous salt, but the copper and sulfate ions remain unchanged—they just reorganize their arrangement.