redissolve

Redissolve refers to the process by which a solid that has formed as a precipitate or crystallized compound dissolves back into a surrounding solvent, returning the system toward a homogeneous solution. It is the reverse of precipitation and crystallization and can occur when solution conditions change to favor dissolution.

Key factors include temperature, pH, solvent composition, and complexation. For many compounds, solubility increases with temperature; heating a saturated solution can cause the solid to redissolve. pH shifts alter speciation; for example, acidifying a metal hydroxide precipitate increases its solubility. Addition of ligands or complexing agents can bind the dissolved ions, forming soluble complexes that pull the solid into solution. Changes in solvent polarity or the presence of chelating agents can similarly promote redissolution. Kinetic factors such as surface area, stirring, and particle size influence how quickly redissolution occurs.

In practice, redissolution is exploited in crystallization control, impurity removal, and formulation reconstitution. A common case is dissolving a metal hydroxide precipitate by adding acid; another is dissolving silver chloride by adding ammonia to form the soluble complex [Ag(NH3)2]+.