Precipitate

Summary: An insoluble solid formed when two solutions are mixed and a reaction occurs. Tags: igcse chemistry definition acids-bases Created: 2026-07-14 Last Updated: 2026-07-14

A precipitate is an insoluble solid that forms and separates from a solution when two aqueous solutions containing soluble salts are mixed and the constituent ions combine to form an insoluble product. Precipitation occurs when the product of the concentrations of the reacting ions exceeds the solubility product of the compound, causing the ions to bond into a solid lattice that settles out of the solution, often appearing as a cloudy suspension. Different precipitates can be identified by their characteristic colours, which makes precipitation a powerful tool in qualitative chemical analysis — for example, silver chloride (AgCl) is white, silver bromide (AgBr) is cream, silver iodide (AgI) is yellow, barium sulfate (BaSO₄) is white, copper(II) hydroxide (Cu(OH)₂) is blue, and iron(III) hydroxide (Fe(OH)₃) is red-brown. Precipitation reactions are widely used in water treatment to remove heavy metal ions, in analytical chemistry for identifying unknown ions in solution, and in industry to manufacture insoluble pigments and to prepare insoluble salts. In IGCSE practical exams, you must be able to describe the colour of a precipitate formed when two named solutions are mixed and write the balanced ionic equation for the precipitation reaction, including the correct state symbols.

Key term — IGCSE Chemistry (0620/0971) glossary.