Question

When does precipitation occur?

Answer 1

Hint :In aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a supersaturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading to precipitation, the chemical reagent causing the solid to form is called the precipitant.

Complete Step By Step Answer:
A precipitation reaction can occur when two solutions containing different salts are mixed, and a cation/anion pair in the resulting combined solution forms an insoluble salt; this salt then precipitates out of solution.
The following is a common example of a precipitation reaction. Aqueous silver nitrate ( $ AgN{O_3} $ ) is added to a solution containing potassium chloride ( $ KCl $ ), and the precipitation of a white solid, silver chloride ( $ AgCl $ ), is observed:
 $ AgN{O_3}(aq) + KCl(aq) \to AgCl(s) + KN{O_3}(aq) $
Here, the product silver chloride is the precipitate, and it is designated as a solid. This reaction can also be written in terms of the individual dissociated ions in the combined solution. This is known as the complete ionic equation:
 $ A{g^ + }(aq) + NO_3^ - (aq) + {K^ + }(aq) + C{l^ - }(aq) \to AgCl(s) + {K^ + }(aq) + NO_3^ - (aq) $
A final way to represent a precipitation reaction is known as the net ionic equation. In this case, any spectator ions are left out of the formula completely. Without the spectator ions, the reaction equation simplifies to the following:
 $ A{g^ + }(aq) + C{l^ - }(aq) \to AgCl(s) $

Note :
Observing precipitation reactions can be useful in the laboratory to determine the presence of various ions in solution. For instance, if silver nitrate is added to a solution of an unknown salt and a precipitate is observed, the unknown solution might contain chloride ( $ C{l^ - } $ ).
Spectator ions are those that do not contribute to the precipitation reaction.