Impurities usually refer to small amounts of chemical substances in a finite quantity of a "host" substance or material. The word "impurities" connotes substances that are present usually in small quantities, but which were probably there to begin with and need to be removed to make the desirable part "pure". One example is hard water, with natural salts as impurities to begin with. But when some coffee is mixed deliberately with a specific aim, the term impurity is grossly inappropriate. It may be termed a solute or, better an ingredient for the preparation of a solution useful for a particular purpose.