The blue color of a copper sulfate solution disappears when aluminum powder is added because of a chemical reaction that occurs between the copper sulfate and the aluminum.
When aluminum is added to the copper sulfate solution, a redox reaction takes place. The aluminum atoms lose electrons and are oxidized, while the copper ions gain electrons and are reduced. The overall reaction can be represented as follows:
3CuSO4(aq) + 2Al(s) → Al2(SO4)3(aq) + 3Cu(s)
In this reaction, aluminum replaces copper in the copper sulfate solution, forming aluminum sulfate (Al2(SO4)3) and elemental copper (Cu). The copper, being a solid, appears as a reddish-brown precipitate, while the aluminum sulfate remains in the solution.
The disappearance of the blue color is due to the removal of the copper ions from the solution, which were responsible for the blue coloration. As copper is reduced and forms a solid, it is no longer present in the solution in its ionic form, resulting in the loss of the blue color.
It's important to note that this reaction is specific to the displacement of copper by aluminum and may not occur in the same way with other metals or compounds.