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Moles, Grams, Formula Weight.
Suppose you go to the pet store and see a pen of 12 puppies:
You then have 1 dozen (12) puppies, 1 dozen (12) puppy noses, 2 dozen (2x12=24) puppy ears, 1 dozen (12)
puppy tails, and 4 dozen (4x12=48) puppy paws.
noses, 2 moles (2 x 6.02 x 1023)of puppy ears, 4 moles (4 x 6.02 x 1023)of puppy paws, etc.
h
This is an ionic compound made of Ca2+ ions and twice as many NO3
 ions.
h
In this chemical formula, we see there is 1 calcium, 2 nitrogens and 6 oxygens.
h
So, if we had 1 mole (6.02 x 1023)of Ca(NO3)2, we would have 1 mole (6.02 x 1023)of calcium atoms, 2
moles (2 x 6.02 x 1023) of nitrogen atoms and 6 moles (6 x 6.02 x 1023)of oxygen atoms.
h
We could also say we have 1 mole (6.02 x 1023)of Ca2+ ions and 2 (2 x 6.02 x 1023) moles of NO3
 ions.
How much would 1 mole (6.02 x 1023 formula units) of Ca(NO3)2 weigh? This value is called the formula
weight or the molar mass. Look on any periodic table. The number under the elemental symbol is the atomic
weight or molar mass of the element. The atomic weight of calcium is 40.08. If you have only one tiny atom of
Ca, it has a mass of 40.08 atomic mass units. If you have 1 mol (6.02 x 1023) of Ca atoms, they would have a
mass of 40.08 grams. To figure out the mass of 1 mol of Ca(NO3)2, just add up the masses of the parts:
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 Spring '08
 Grise

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