12/11/2013
Percent Composition
Any sample of a pure compound always consists of the same
elements combined in the same proportions by mass.
This means molecular composition can be expressed in at least
three ways:
In terms of the number of atoms of each type per molecule or
formula unit; the formula of the compound
In terms of the mass of each element per mole of compound
In terms of the mass of each element in the compound relative to
the total mass of the compound; mass percent
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12/11/2013
Let’s assume you have1.000 mol of NH3 or 17.03 g. The mass of NH3
is composed of:
14.01 g of N (1.000 mol)
3.024 g of H (3.000 mol)
If you compare the mass of N to the
total mass of compound
82.27% of the total mass is N
17.76% of total mass is H
How to determine the percent composition
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