green solution of ferrous sulphate was taken in four separate test tube mark 2 1 2 3 and 4 pieces of copper zinc and Aluminium dropped in test tube 1 2 3 and 4 respectively in which cases
(a)colour of ferrous sulphate solution will match with the colour in test tube one give reason
(b)colour of ferrous sulphate solution will fade and black mass will be deposited on the surface of the metal?
Answers
Change in colour of green ferrous sulphate solution in each case :
(a) The colour of ferrous sulphate solution will match with the colour in test tube 1 because no reaction will take place in test tube 1.
• Test tube 1 contains a mixture of copper pieces and green ferrous sulphate solution.
• Since copper is placed below iron in the reactivity series of metals, it cannot displace iron from its solution.
• Therefore, no reaction takes place in test tube 1, and the colour of the ferrous sulphate solution remains as it is, green.
• The reaction can be represented as under :
FeSO₄ (green) + Cu → No reaction (green)
(b) The colour of ferrous sulphate solution fades from green to colourless and black mass gets deposited on the surface of test tubes 2 and 3.
• Test tube 2 contains pieces of zinc mixed with ferrous sulphate solution, and test tube 3 contains pieces of aluminum mixed with ferrous sulphate solution.
• Both zinc and aluminum are more reactive than iron as they are placed above iron in the reactivity series of metals.
• Therefore, they can easily displace iron from its solution, and take its place in the same.
• As a result, colourless zinc sulphate is formed in test tube 2 and colourless aluminum sulphate is formed in test tube 3, depositing the black iron metal on the surface of each test-tube.
• Therefore, reaction in test tube 2 proceeds as follows :
FeSO₄ (green) + Zn → ZnSO4 (colourless) + Fe (black)
• Reaction in test tube 3 takes place as follows :
3FeSO₄ (green) + 2Al → Al₂(SO₄)₃ (colourless) + 3Fe (black)