The Mole
A mole is a unit for counting atoms, molecules, ions, electrons, etc. It is used in the same sense
that a dozen is a convenient unit for donuts, eggs, etc.
One dozen is a small integer number because donuts, eggs, etc, are large objects. One mole is a
large integer because atoms, molecules, ions, electrons, etc, are really small objects.
The international convention is that a mole is equal to the number of atoms contained in an
exactly 12 gram sample of pure
12
C isotope. With this definition of a mole we further define:
Gram Atomic Weight:
weight of one mole of atoms. For example, Carbon has a gram atomic weight of 12.011
Gram Molecular Weight:
weight of one mole of molecules. For example, CO
2
has a gram molecular weight of
44.01
Gram Formula Weight:
weight of one mole of a given stoichiometry. For example, NaCl has a gram formula
weight of 58.44. NaCl is not really a molecule so we use the more general term formula.
Concentration Units
Molarity
A concentration given in units of molarity is calculated according to:
The unit volume is most commonly in liters. The abbreviation for molarity is
M
.
helpful hint:
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 Winter '08
 FOUCHER
 Chemistry, Molecule, gram molecular weight, gram formula weight, gram atomic weight

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