precipitaties

Precipitaties, commonly referred to as precipitates, are solid substances that form in a liquid medium as a result of a chemical reaction or a change in solubility that reduces the dissolved ion concentration below its solubility limit. In aqueous solutions, most precipitates arise from precipitation reactions in which two soluble salts react to produce an insoluble salt and a soluble counterion. Typical examples include silver chloride (AgCl), barium sulfate (BaSO4), and calcium carbonate (CaCO3).

Formation involves nucleation and crystal growth. Nucleation can be homogeneous, occurring uniformly in the solution, or heterogeneous, occurring on surfaces or impurities. Growth depends on factors such as supersaturation, temperature, pH, ionic strength, and the presence of complexing agents, which influence the size, morphology, and purity of the precipitate.

Solubility equilibria are described by the solubility product constant (Ksp). A precipitate forms when the product of ion concentrations in solution exceeds the Ksp (the ion product Q is greater than Ksp). Temperature and common ions can shift solubility; most sparingly soluble salts become less soluble with decreasing temperature, though there are exceptions.

Separation and purification commonly use filtration, decantation, or centrifugation to collect the solid, followed by washing to remove soluble impurities and drying to obtain the solid material in a usable form.

Applications include qualitative and quantitative inorganic analysis, synthesis of inorganic salts, pigments, catalysts, and materials science. Precipitation reactions are also used to remove contaminants from water and to drive selective crystallization in synthesis.