Magnesium metal reacts with copper sulfate solution but not with copper sulfate solution because of the presence of dissolved oxygen in the water. Oxygen acts as a protective barrier on the surface of the copper metal, preventing it from coming into direct contact with the magnesium. This barrier prevents the magnesium from oxidizing and forming magnesium oxide, which would inhibit the reaction between magnesium and copper sulfate.

Inert Atmosphere Experiment:

To demonstrate this effect, you can perform the following experiment:

Take two containers and fill them with copper sulfate solution.

Place a piece of magnesium metal in each container.

Bubble pure nitrogen gas into one of the containers to create an inert atmosphere.

Observe the containers over time.

In the container with the dissolved oxygen, you will notice a reaction between the magnesium and the copper sulfate solution. The magnesium will begin to dissolve, and the solution will turn blue due to the formation of copper ions.

However, in the container with the inert atmosphere, there will be no reaction between the magnesium and the copper sulfate solution. The magnesium will remain intact, and the solution will remain clear.

This experiment clearly shows that the presence of dissolved oxygen in the water is necessary for the reaction between magnesium and copper sulfate solution.