There are around 90 natural occuring elements on earth and they combine in varying ways to produce thousands of compounds. Hydrogen and oxygen, for example, form water and sodium and chlorine form sodium chloride, commonly called table salt. Most of the things around us, however, aren't simply pure compounds, but rather, a mixture of compounds. Unless you are using distilled water, any sample obtained from a river, lake, or even a well will be a mixture of water with a variety of minerals dissolved in it. Look on any label of any household product, and you will see a listing of its ingredients. Seldom will you see simply one thing listed. More often than not, there will be several substances listed.
It is important to know the four main ways in which mixtures differ from compounds. The following chart shows these ways. It also lists the ways one may tell if a chemical reaction is occuring.
Send questions, comments or suggestions to
Gwen Sibert, at the
Roanoke Valley Governor's School
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