A variety of units can be used to measure the concentration of solute in a solution. In general, a concentrated solution is one where the amount of solute in a given volume of solvent is great. A dilute solution is one where the amount of solute in a given volume of solvent is relatively small. But can we mix up a solution of any concentration? For example, can we produce a 90% solution of table salt in water? How about a 90% solution of table salt in gasoline?

A few substances are infinitely soluble, or miscible, which means that they can be mixed together in any proportion. Ethyl alcohol and water are an example of miscible substances since they can be mixed together in concentrations ranging from pure alcohol to pure water. However, most substances are not infinitely soluble.

Solubility is a term used to describe the amount of solute which can be dissolved in a solvent. The solubility of two substances will depend on the similarity of the two substances. As mentioned on the last page, some substances (such as oil and water) have a solubility of close to zero. Most substances, however, will have a solubility somewhere between complete insolubility and complete miscibility.