Precipitation (chemistry)
In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a supersaturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading to precipitation, the chemical reagent causing the solid to form is called the precipitant.
Illustration of the Walden reductor. Copper from a wire is displaced by silver from a silver nitrate solution it is dipped into, and metallic silver crystals precipitate onto the copper wire.
Crystals of meso-tetratolylporphyrin from a reflux of propionic acid precipitate on cooling. Photograph of the Büchner funnel on top of a Büchner flask.
Solvation describes the interaction of a solvent with dissolved molecules. Both ionized and uncharged molecules interact strongly with a solvent, and the strength and nature of this interaction influence many properties of the solute, including solubility, reactivity, and color, as well as influencing the properties of the solvent such as its viscosity and density. If the attractive forces between the solvent and solute particles are greater than the attractive forces holding the solute particles together, the solvent particles pull the solute particles apart and surround them. The surrounded solute particles then move away from the solid solute and out into the solution. Ions are surrounded by a concentric shell of solvent. Solvation is the process of reorganizing solvent and solute molecules into solvation complexes and involves bond formation, hydrogen bonding, and van der Waals forces. Solvation of a solute by water is called hydration.
Nile red at daylight (top row) and UV-light (second row) in different solvents. From left to right: 1. Water, 2. Methanol, 3. Ethanol, 4. Acetonitrile, 5. Dimethylformamide, 6. Acetone, 7. Ethylacetate, 8. Dichlormethane 9. n-Hexane, 10. Methyl-tert-Butylether, 11. Cyclohexane, 12. Toluene. Photographer: Armin Kübelbeck, CC-BY-SA, Wikimedia Commons