The mole fraction and mass percent are widely used in non-chemical sciences. In evironmental and health sciencies the part per million (ppm) is widely used for trace compounds in the environment. The ppm is formally a mass fraction and so should be corrected by the molar mass before application in the analytical laboratory. Sometimes the ppm in the atmosphere is treated as a volume fraction (and then by Dalton's law a mole fraction). This usage can introduce error since the molar mass of gases are not identical. In this section we discuss the strategies for converting to and fraom essentially every unit of concentration. If you need to review the definitions of concentration click here.
