Metal displacement reaction. Copper coin that is half coated with a layer of silver, having been dipped in a solution of silver nitrate (AgNO3). Copper is a more reactive metal than silver. Over time, copper displaces (replaces) the silver in the solution to form a blue solution of copper nitrate (Cu(NO3)2, lower right). The silver that has been displaced out of solution crystallizes as a solid black coating on the coin. The formula for this reaction is: Cu + 2AgNO3 ---> Cu(NO3)2 + 2Ag.