Copper sulfate turns green when iron is added because of a single displacement reaction, where iron displaces copper from the copper sulfate solution. Here's the breakdown:

1. Initial state: Copper sulfate (CuSO₄) is a blue solution, and iron (Fe) is a solid metal.

2. Reaction: When iron is added to the copper sulfate solution, it reacts with the copper ions (Cu²⁺) in the solution. Iron is more reactive than copper, meaning it loses electrons more easily. This leads to the following reaction:

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

3. Result: The reaction produces iron(II) sulfate (FeSO₄), which is a light green solution, and solid copper (Cu) is deposited on the surface of the iron.

The green color comes from the iron(II) sulfate solution formed. The copper ions in the original solution have been replaced by iron ions, giving the solution its characteristic green color.

Additional points:

* The reaction is also known as a redox reaction, involving the transfer of electrons. Iron is oxidized (loses electrons), and copper is reduced (gains electrons).

* The reaction is a clear demonstration of the reactivity series of metals, which indicates the relative ease with which metals lose electrons. Iron is higher in the series than copper, making it more reactive.

* The green solution can eventually turn brown due to the oxidation of iron(II) sulfate to iron(III) sulfate (Fe₂(SO₄)₃).

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