Liquids and solids are examples of condensed states of matter. Chemists imagine the molecules in liquids to be touching, shoulder to shoulder. Liquids and gases are examples of fluids. For example, both liquids and gases can be poured from one container to another, and can flow through a tube or pipe. Liquid water is the most commonly found fluid on the earth's surface.

A solution is a homogeneous mixture of two or more substances. By homogeneous we mean that only a single phase can be detected when the solution is examined visually or even with an optical microscope. For reasons discussed below, most of the water on earth's surface really is not pure, but instead consists of solutions in which water has acted as a solvent and dissolved other substances, solutes. To a slight degree, the nitrogen, oxygen, and argon of air are water soluble.

This course is devoted to liquids and solutions, with an emphasis on water. It assumes that you've already studied a considerable amount of chemistry -- and does not "begin at the beginning."