Difference and similarity between AW, MW and FW and molar mass

[robert zellmer]

I've received a couple of questions about exactly what is atomic weight,
molecular weight and formula weight and molar mass when to use
amu or g/mol, etc.  Here's what I've got.

As pointed out in lecture, the terms AW , MW and FW are used when 
referring to the
average mass of a SINGLE atom, molecule or f.u. (formula unit for ionic 
cmpds) and
the unit for this is amu (a single atom, molecule or formula unit has a 
very small mass
in grams so we use amu).  The molar mass is the mass in grams of a MOLE 
of atoms,
molecules or f.u. and the unit is g/mol.  The numbers are the same. For 
example, 1 H
atom has an average mass of 1.01 amu and 1 mole of H atoms has an 
average mass of
1.01 grams.  For a  molecule it's very similar.  For H2O, a single 
molecule has a mass
of 18.02 amu (the MW) while a mole of H2O molecules has a mass of 18.02 
g.  So the
molar mass and AW, MW  and FW mean something different but the number is 
the same.

Hope that makes sense.

Dr. Zellmer