In chemistry, a precipitate is a solid that forms from a solution when two or more reactants combine. Precipitation occurs when the concentration of the dissolved substance exceeds the solubility limit of the solvent. The solid particles that form are called a precipitate, while the remaining liquid is called the supernatant liquid.

Precipitation is a common technique used in the separation and purification of compounds. By carefully controlling the conditions of the reaction, it is possible to selectively precipitate out one or more components of a mixture. This can be achieved by adjusting the temperature, pH, or concentration of the reactants.

Precipitates can also be used to identify different substances. When a known reagent is added to a solution, the formation of a precipitate can indicate the presence of a specific compound. This is a common technique used in qualitative analysis.

Some examples of precipitation reactions include:

* the formation of silver chloride when silver nitrate is added to a solution of sodium chloride

* the formation of calcium carbonate when calcium hydroxide is added to a solution of sodium carbonate

* the formation of iron(III) hydroxide when iron(III) chloride is added to a solution of sodium hydroxide