Question

Why does the iron nail become brownish in colour and the blue colour if the copper sulphate solution fades?

Answer 1

hey
this is your answer
when you are dipping a iron nail in CuSo4 solution then the Iron metal displaces copper metal from its compound copper sulphate. it is the copper metal set free from its compound which forms red brown layer on the surface of iron nail..
hope this answer will helpful to u

Answer 2

When an iron nail immersed in the solution of copper sulphate than iron displaces copper from the solution of copper sulphate because iron is more reactive than copper. Therefore copper sulphate solution colour changes from blue to pale green.