Question #0417a

1 Answer

Mass of molecule = Weight of molecule in Atomic Mass Units (AMU)
Gram Molecular Mass = Weight of one mole of molecules


To measure the mass of molecules, the measure used is the Atomic Mass Unit, or AMU. An atomic mass unit is precisely #1/12# of the mass of one atom of carbon-12, an isotope of carbon. Because carbon-12 has 6 protons and 6 neutrons, one AMU can be roughly defined as the combination of the mass of protons plus neutrons in an atom. Based on this, we find that carbon-12 has an AMU of 12.

The gram molecular mass is the mass of one mole of molecules. A mole is defined as "the amount of a chemical substance that contains as many representative particles, e.g., atoms, molecules, ions, electrons, or photons, as there are atoms in 12 grams of carbon-12" (wikipedia/wiki/Mole_(unit). This means that carbon-12 has a mole of one, and a gram molecular mass of 12 g, by definition.

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