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

Copper sulphate crystal is blue. So it is also called "Blue Vitriol". Refining industries use it to refine impurities from metals and as a fungicide in agriculture. It dissolves in water and forms a blue solution.

The iron metal reacts with copper sulphate and displaces copper.

CuSO4(aq) + Fe(s) -------> FeSO4(aq) + Cu(s)

Ferrous sulphate form is colourless. As a result, the solution changes its colour.

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