When an iron bar is dipped into silver nitrate a coating of dendrite-like silver particles will deposit on the surface of the iron. The solution, which starts out colorless, will begin to have a light green color. The mass of the iron bar will decrease.
This is a single replacement (also called single displacement) reaction. It occurs because iron is more reactive than silver. The solution initially contains Ag+ ions and NO3- ions. When the Ag+ ions come into contact with the iron electrons are transferred from iron to silver. This produces neutral silver metal which isn't soluble and Fe2+ ions which dissolve in solution to give a green color. Iron has "replaced" or "displaced" silver in the nitrate compound. Evaporation of the resulting solution would produce solid iron(II)nitrate.
Here's the equation for this reaction:
`Fe + 2AgNO_3 -> 2Ag + Fe(NO_3)_2`