Purpose: To become familiar with the methods of separating substances from one another using decantation, extraction, and sublimation techniques.
Apparatis and Chemicals: balance, Bunsen burner, rubber hose, tongs, 2 evaporating dishes, 2 watch glasses, 100-mL graduated cylinder, clay triangles, 2 ring stands, 2 iron rings, 2 glass stirring rods, unknown mixture of NaCl, NH4Cl, SiO2.
Discussion: Mixtures are composed of two or more substances mixed together. Mixtures can be homogeneous, or uniformly distributed; they can also be heterogeneous, or not uniformly distributed. The components of a mixture remain chemically unchanged. They are merely physically mixed. Therefore, it is possible to separate them. There are several ways to separate substances, depending on the properties of the substances. Some substances dissolve when placed in water. These substances are soluble in water. Others are unchanged when placed in water. These substances are insoluble in water. Thus, if a soluble substance is mixed with an insoluble substance, separation through decantation can take place. Decantation involves pouring water onto a mixture and stirring. The soluble substance will dissolve, leaving the insoluble one intact. The newly-formed aqueous mixture of water and the soluble substance can be poured into a separate container and heated so that the water evaporates. The substance have now been separated without any changes to the elemental composition of the substances. Decantation is usually performed more than once on the insoluble substance to ensure that all particles of the soluble substance have been removed.
Some substances can pass directly from the solid to the gaseous stage without first melting and becoming liquid. These substances are said to be able to sublime. Substances that sublime, when mixed with substances that do not sublime, can be separated by heating the mixture until the substance that can...