Related Quantities
Molar mass is closely related to the relative molar mass (M
r) of a compound, to the older term formula weight, and to the standard atomic masses of its constituent elements. However, it should be distinguished from the molecular mass (also known as molecular weight), which is the mass of one molecule (of any single isotopic composition) and is not directly related to the atomic mass, the mass of one atom (of any single isotope). The dalton, symbol Da, is also sometimes used as a unit of molar mass, especially in biochemistry, with the definition 1 Da = 1 g/mol, despite the fact that it is strictly a unit of mass (1 Da = 1.660 538 782(83)×10−27 kg).
Molecular weight (M.W.) and formula weight (F.W.) are older terms for what is now more correctly called the relative molar mass (M
r).Nic, M.; Jirat, J.; Kosata, B., eds. (2006–). "relative molar mass". IUPAC Compendium of Chemical Terminology (Online ed.). doi:10.1351/goldbook.{{{file}}}. ISBN 0-9678550-9-8. http://goldbook.iupac.org/R05270.html. This is a dimensionless quantity (i.e., a pure number, without units) equal to the molar mass divided by the molar mass constant.
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