Laboratory 6.0: Separating Mixtures – Introduction


This article incorporates, in modified form, material from Illustrated Guide to Home Chemistry Experiments: All Lab, No Lecture.


A mixture is a substance that comprises two or more elements and/or compounds that are physically intermingled but that have not reacted chemically to form new substances. A mixture may be a solid, liquid, gas, or some combination of those states.

We are surrounded by mixtures, both in the chemistry lab and in everyday life. The air we breathe is a mixture of nitrogen, oxygen, and small amounts of other gases. Our soft drinks are complex mixtures of water, sugar, carbon dioxide, and various organic compounds that provide color and flavor. The foods we eat are complex mixtures of organic and inorganic compounds.

Mixtures are often created intentionally because a desirable characteristic is sought. For example, stainless steels are mixtures of iron, chromium, carbon, nickel, manganese, and other elements in specific proportions, chosen to optimize characteristics such as resistance to corrosion, hardness, tensile strength, color, and luster. Similarly, concretes are complex mixtures of components chosen to minimize cost while optimizing strength, durability, resistance to road salts, permeability to water, and other factors, depending on the purpose for which the concrete will be used.

Because the components of a mixture have not reacted chemically, it is possible to separate the mixture into its component substances by using purely physical means. Chemists have devised numerous methods for separating compounds based on differential physical characteristics, including differential solubility, distillation, recrystallization, solvent extraction, and chromatography. In this section, we’ll examine these common methods for separating mixtures.

August 24, 2009