Why so some mixtures of ionic compounds form a solid precipitate?

When two solutions of ionic compounds are mixed, they may react to form a solid precipitate if the resulting product is insoluble in water. This occurs when the ions in the two solutions combine to form a new compound that has a low solubility product constant, causing the compound to precipitate out of solution as a solid. Factors such as the nature of the ions and their charges determine if a precipitate will form.