Why does the colour of copper sulphate solution changes when an iron nails is dipped in it?
Iron is more reactive than copper. Therefore, when an iron nail is dipped in a copper sulphate solution, the iron displaces copper from its copper sulphate solution. This leads to formation of iron (I) sulphate which causes the colour of the solution to change from blue to green.
Copper sulphate solution is blue in colour but when iron is dipped into it, the iron displaces copper from its salt solution and copper sulphate solution changes to greenish colour.