Question

Why does the colour of copper sulphate solution change when an iron nail is dipped in it ?

Answer 1

because in this reaction iron displaces copper

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)