Try Phase Change Separations

Second step in classification [1flowch3.gif] The next question to ask is whether the material can be separated into components by using phase change methods such as distillation. Materials which are separated into components when they go through distillation or sublimation or some other phase change are classified as "homogeneous mixtures" or "solutions." Materials which are not broken up into components or separated into components by going through phase change operations are classified as "pure substances."

The distillation of water can serve as an example. If the water has something dissolved in it (making it a solution), distillation will evaporate the water and leave the other component behind. Seeing this, we know that there were two (or more) components in the original material and thus it must have been a mixture. On the other hand, if nothing was dissolved in the water, distillation would not separate anything from the water. Seeing this, we know that the water was pure and was not a mixture.

Note that we now have two categories of mixtures, heterogeneous mixtures and homogeneous mixtures. Because homogeneous mixtures are usually called solutions, heterogeneous mixtures are sometimes simply called mixtures. Keep in mind that a material which is referred to as a mixture might be homogeneous or heterogeneous.

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E-mail instructor: Sue Eggling