Question

why does the colour of copper sulphate solution change when an iron nail is dipped in it write 2 observation

Answer 1

1- copper sulphate solution colour change from blue to
green colour....
2-the nail gets coated with copper so it becomes brownish...

Answer 2

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When an iron nail dipped in the copper sulphate solution than iron displaces copper from the copper sulphate because iron is more reactive than copper. Therefore the colour of the copper sulphate solution changes.

The reaction involved here is:

Fe (s) + CuSO4 (aq) → FeSO4 (aq) + Cu (s)