precipitante

A precipitant, in chemistry, is a substance that promotes the formation of a solid from a solution, known as a precipitate. Precipitation takes place when the solubility of one or more dissolved species is exceeded, causing an insoluble salt or compound to separate from the solution. The precipitant can act by supplying a component of the insoluble salt, by altering the solution conditions (such as pH or redox state), or by forming a complex that reduces the solubility of the target species.

In inorganic analytical chemistry, precipitants are selected to selectively remove a particular ion. For example, silver nitrate can act as a precipitant for halide ions to form AgCl, while barium salts can precipitate sulfate as BaSO4. Calcium ions can be precipitated as calcium carbonate or calcium phosphate by carbonate or phosphate precipitants, respectively. The effectiveness of a precipitant depends on the low solubility of the resulting salt, the absence of competing precipitates, and the stability of the precipitate under the reaction conditions.

In biochemistry and protein chemistry, precipitants such as ammonium sulfate, polymers, or organic solvents are used to reduce protein solubility and induce aggregation and sedimentation. Precipitation is also used in crystallization processes, environmental chemistry, and wastewater treatment.

Key considerations when selecting a precipitant include the desired selectivity, the tolerance of other ions in the mixture, the pH and temperature sensitivity, and the ease of recovering or removing the precipitate. Safety and compatibility with analytical or preparative goals are essential in choosing an appropriate precipitating agent.