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Molecular weight (MW) is the mass of one mole of a chemical entity. In other words, MW is the sum of the masses of the atoms making up a molecule. It is expressed in atomic mass units (a.m.u) or Dalton (Da). However, it is common to annotate it without units.

This data is systematically annotated on powder bottles, as it is essential for adjusting the molarity of a solution. However, there are various acronyms for molecular weight. In French, it’s PM (Poids Moléculaire), while in English it’s MW (Molecular Weight) or FW (Formula Weight).

Molecular weight can be used to determine the molar mass (M) of a chemical species. 1 a.m.u = 1Da = 1g.mol-1. Below is a video, from TheChemistryNinja, showing how to calculate molecular weight (or molar mass).