Q. Crystals of a compound changes its blue color to white on heating in a closed container. However, it regains blue color after sometime when allowed to cool down. This compound is of which of the following metals?
Answer: Copper
Notes: The compound is pentahydrate copper sulphate. Its chemical formula is CuSO4. 5H2O and is known as Blue Vitriol. It is blue crystalline solid and becomes dirty white on heating due to the loss of water molecules and finally becomes amorphous. It regains its colour by absorbing water from atmosphere and becomes blue again.

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