Precipitation reaction

A precipitation reaction forms an insoluble solid from dissolved species in a solution. The solid product, called a precipitate, separates from the liquid phase.

Solubility product: The equilibrium constant for the dissolution of a sparingly soluble ionic solid into its constituent ions. Comparing the ion product with this constant predicts whether a precipitate can form.
Solubility: The amount of a substance that dissolves in a specified solvent under defined conditions. A precipitate forms when dissolved amounts exceed the relevant equilibrium solubility.
Qualitative inorganic analysis: The identification of inorganic ions through characteristic chemical reactions and observations. Selective precipitates reveal which ions are present in an unknown sample.
Silver chloride: A white ionic solid with formula AgCl that is sparingly soluble in water. Its formation from silver and chloride ions is a standard precipitation example.
Ionic product: The product of dissolved-ion concentrations, each raised to its stoichiometric power in a dissolution equation. It indicates whether a solution is undersaturated, saturated, or supersaturated relative to a solid.
Ionic compound: A substance composed of positively and negatively charged ions held together by electrostatic attraction. Many precipitates are ionic solids assembled from oppositely charged dissolved ions.
Gravimetric analysis: A quantitative analytical method that determines an analyte’s amount from the mass of a measured product. A precipitate can be isolated, purified, and weighed to calculate analyte concentration.
Barium sulfate: A white, highly insoluble ionic solid with formula BaSO₄. Its low solubility makes it a clear example and a useful gravimetric product.
Supersaturation: A condition in which a solution contains more dissolved solute than its equilibrium solubility permits. Precipitation becomes thermodynamically favorable once the solution is supersaturated.
Aqueous solution: A homogeneous mixture in which water is the solvent and other substances are dissolved. It is the liquid medium in which most introductory precipitation reactions occur.

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