So 100 g
of this substance has 63.57 g of carbon, 6 g of hydrogen, 9.267 of nitrogen,
and 21.17 of oxygen.
I need to
have them all in moles (n). You can find the molar mass (M) of each element in
a periodic table.
n = m/M
63.57 g C
-> 63.57 g C/12.01 g/mol = 5.29 moles C
6 g H
-> 6 g C/1.008 g/mol = 5.95 moles H
9.267
g N -> 9.267 g N/14.01 g/mol = 0.6615 moles N
21.17
g O -> 21.17/16.00 g/mol = 1.32 moles O
So
the minimum formula has this rate:
C
5.29 H 5.95 N 0.6615 O 1.32
Now you should divide all those numbers by
the smallest one (1.32):
C 4 H 4.5 N 0.5 0 1
Now it looks a lot more like a molecular
formula… but we still have fractions.
Let’s multiply all numbers by 2:
C8H9N1O2
<span>Now they are all whole numbers!
</span>
So the minimum formula
is C8H9NO2
The minimum
formula is not always equal to the molecular formula… but in this case, I found
there is a molecular formula with this same numbers, and it’s called acetaminophen.
