precipitation

In chemistry, the formation of an insoluble solid in a liquid as a result of a reaction within the liquid between two or more soluble substances. For example, if solutions of lead nitrate and potassium iodide are added together, bright yellow, insoluble lead iodide appears as a precipitate in the solution, making it cloudy. The precipitation reaction is: lead nitrate + potassium iodide → lead iodide + potassium nitrate. If the newly formed solid settles, it forms a precipitate; if the particles of solid are very small, they will remain in suspension, forming a colloidal precipitate.

Precipitation reactions are used in the preparation of salts; in qualitative analysis reactions; and in the formation of some sedimentary rocks.