Question

2. A colorless crystalline compound when dissolved in water formed a colorless solution . This compound was heated in a clean, dry test tube. This heating produced several drop- lets of water on the upper region of the test tube. The residue was dissolved in water and formed a yellow-brown solution. a. Determine if this colorless crystalline compound is a true hydrate or not. b. Give reasons.

Answer 1

a) This colorless crystalline compound is not a true hydrate.

b) Any true hydrate would lose its hydration molecules on heating. But, when this residue is dissolved in water, it does not form a different colored solution. This is because true hydrates have reversible property of hydrate molecules, according to which the anhydrous compound on dissolving in water simply regains its hydration molecules and forms a colored solution of the original crystalline compound rather than a different colored solution.