Precipitation refers to the process whereby a solid forms and separates from a liquid solution, typically as a result of a chemical reaction. When certain ions in a solution exceed their solubility, they will combine to form a solid (the precipitate), which can then settle out of the solution. This is a key concept in water quality analysis as it can indicate the presence of certain substances in water and how they interact with each other.
While other processes and changes of state are discussed in different contexts, they do not describe the formation of solid particles that occurs during precipitation. For example, dissolving a solid into a liquid is a distinct process where the solid becomes part of the solution, rather than forming a separate solid. Similarly, the change of a liquid into gas pertains to evaporation or boiling, which is not related to the formation of a solid from a liquid. The removal of impurities from solutions can encompass a variety of processes but does not specifically refer to the chemical formation of solids from liquids as is characteristic of precipitation.