Aqueous Solutions: Concentration

Most chemical reactions reaction occur in a liquid solvent/solute (i.e., solution) environment. Typically the solute(s) in a solution will be the reactants. Since stoichiometric calculations require amounts of reactants, we need a way to express amounts of reactants when they are in solution. The way chemists do this is through the concept of concentration. Concentration is a way to express the amount of solute per unit amount of solution/solvent. There are several ways that concentration can be expressed. A few of these are:

ppm (parts per million) ppb (parts per billion) weight/weight percent (w/w%) weight/volume percent (w/v%) volume/volume percent (v/v %) percent by mass molarity

All of these concentration units have their applicability. In the following pages we will discuss and exemplify these units.