Question

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

Answer 1

This is because the sulphate from the copper sulphate solution is deposited on iron which makes the iron nails brown and the solution may change to colourless

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)