Introductory University Chemistry I. Dissolution, Evolution, and Precipitation Introductory University Chemistry I Solutions and Solubility Dissolution, Evolution, and Precipitation Pure substances, whether elements or compounds, are rarely found in nature and can often be obtained only with considerable difficulty. Most materials we encounter are mixtures of two or more substances. When a mixture is homogeneous, it is called a solution. A mixture of grains of sand and grains of salt is not homogeneous, while a mixture of salt and water forms a homogeneous mixture or solution when enough water is present to form a homogeneous mixture with, or to dissolve, all of the salt present. Likewise, gases dissolve in liquids to form solutions.
Fish can survive in water by using their gills to extract the dissolved oxygen.
Much of the world around us is made up of aqueous solutions. The oceans and our blood are only two of many examples. We now take up some of the aspects of solutions will be considered, with emphasis on solutions in that almost ubiquitous solvent, water. The same concepts apply equally well to solutions which are not aqueous. The process of dissolution occurs when a solute is placed in contact with a solvent and dissolves to form a solution.