Metal displacement reaction. Image 1 of 2. Magnesium ribbon reacting with copper sulphate (CuSO4, blue) in a displacement reaction. Magnesium (Mg) is a more reactive metal than copper (Cu). Over time, the magnesium displaces (replaces) the copper to form a colourless solution of magnesium sulphate (MgSO4). The copper that has been displaced out of solution crystallizes as a solid and sinks to the bottom. The formula for this reaction is: Mg + CuSO4 ---> MgSO4 + Cu. For an image at the end of the reaction, see image A500/264.