Question

Blue coloured crystals of a substance “X” on heating loses
its colour on heating , but regains the colour when water is
added into it. Explain why?

Answer 1

Answer:

The blue colour of crystals of a substance changed on heating in a closed test tube but the colour was regained after sometime on cooling. Name the substance and write irts chemical formula. Explain the phenomenon invilved. <br> (b) Write name and chemical formula of two such compounds whose one formula unit is associated with 10 and 2 water molecules respectively.

Answer 2

Blue coloured crystals of a substance “X” on heating loses  its colour on heating, but regains the colour when water is  added into it due to the following:-

• The given substance X is hydrated copper sulphate which has a molecular formula of CuSO₄.5H₂O
• The fixed number of water molecules attached to the formula unit of a particular salt is termed water of crystallisation of the salt.
• But when it is heated, it will lose its water of crystallisation and the anhydrous copper sulphate is white in colour.