Selective Precipitation of Ions. Selective precipitation is a technique of separating ions in an aqueous solution by using a reagent that precipitates one or more of the ions, while leaving other ions in solution. Qualitative Analysis for Metallic Elements.Click to see full answer. Thereof, what is selective precipitation used for?Selective precipitation of proteins can be used as a bulk method to recover the majority of proteins from a crude lysate, as a selective method to fractionate a subset of proteins from a protein solution, or as a very specific method to recover a single protein of interest from a purification step.Secondly, what would precipitate first? When two anions form slightly soluble compounds with the same cation, or when two cations form slightly soluble compounds with the same anion, the less soluble compound (usually, the compound with the smaller Ksp) generally precipitates first when we add a precipitating agent to a solution containing both anions (or Moreover, what is a precipitation reaction? A precipitation reaction is a type of chemical reaction in which two soluble salts in aqueous solution combine and one of the products is an insoluble salt called a precipitate. Note that not all ionic compounds react to form precipitates. Also, a precipitate may form under certain conditions, but not others.What is a precipitate and how is it formed?A precipitate is a solid formed when the cation and anion in an aqueous solution react to form an insoluble compound. An ionic solution is when the ions of a compound have dissociated in an aqueous solution.