question_answer

   (i) Crystals of copper sulphate are heated in a test tube for some time. What is the colour of copper sulphate crystals before heating, and after heating? What is the source of liquid droplets seen on the inner upper side of the test tube during the heating process?          (ii) A metal 'X' when dipped in aqueous solution of aluminium sulphate no reaction is observed whereas when it is dipped in an aqueous solution of ferrous sulphate, the pale green solution turns colourless. Identify metal 'X' with reason. [CBSE (AI) 2009]  

Answer:

                  (i) (a) Blue; white (b) The liquid droplets are actually the           water droplets. The source of water droplets is the water of crystallization of hydrated copper sulphate crystals (CuSO4.5H2O). (ii) When metal 'X' is dipped in aqueous solution of aluminium sulphate no reaction is observed, it means it is less reactive than aluminium. But when it is dipped in ferrous sulphate solution, the solution turns from pale green to colourless, so 'X' is more reactive than iron and thus displaces it from its solution. Therefore, 'X' must be zinc. It reacts with ferrous sulphate to form colourless zinc sulphate solution by displacing iron.                 Zn(s) + FeSO4(aq)  ZnSO4(aq) + Fe(s)