A precipitation reaction is a type of reaction when two solutions react to form an insoluble solid (ionic salt)
A lot of ionic compounds dissolve in water and exist as individual ions. But when two ions find each other forming an insoluble compound, they suddenly combined and fall to the floor.
Once the sediment is made, it becomes an irreversible reaction because it is hard to ionize and dissolve again.
The sediment generation reaction can be used to determine the types of ions in an unknown solution.
Some sediment generation reactions are below.
| Na+ | K+ | Ba2+ | Ca2+ | Pb2+ | Ag+ | |
| Cl– | – | – | – | – | White | White |
| S2- | – | – | – | – | Black | Black |
| NO3– | – | – | – | – | – | – |
| SO42- | – | – | White | White | White | White |
| CO32- | – | – | White | White | White | Bright Yellow |
| I– | – | – | – | – | Yellow | Yellow |
| Br– | – | – | – | – | White | Bright Yellow |