A reddish pink substance on heating gives off a vapour which condenses on the sides of the test tube and the substance turns blue. It on cooling water is added to the residue it turns to its original

Question

A reddish pink substance on heating gives off a vapour which condenses on the sides of the test tube and the substance turns blue. It on cooling water is added to the residue it turns to its original colour. The substance is:

Prashant Kotian · Accepted Answer

Correct answer: C. Step 1: Cobalt(II) chloride hexahydrate (CoCl2.6H2O) exists as reddish-pink crystals. Step 2: Upon heating, it loses its water of crystallization to form anhydrous cobalt(II) chloride, which has a deep blue color: CoCl2.6H2O (pink) --Δ--> CoCl2 (blue) + 6H2O (vapour). Step 3: When water is added back to the blue anhydrous residue, it readily rehydrates to restore the pink hexahydrate, CoCl2.6H2O. This matches option (c).

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