In a precipitation reaction (otherwise known as a double replacement or metathesis reaction) the extent to which a precipitate is formed is dependent on the solubility product constant of the precipitate. A species with a large Ksp (highly soluble) may not precipitate until very high concentrations are reached. A species with a low Ksp (mostly insoluble) will precipitate readily. Use the ideas explored in this activity to explain why the formation of a precipitate may increase when non-stoichiometric amounts of reactants are used (one reactant will limit, while the other will be in excess).