Serotonin (molar mass 176 g/mol) is a compound that conducts nerve impulses in brain and muscle. It contains 68.2% C, 6.86% H, 15.9% N and 9.08% O. What is the molecular formula?
As with all these problems, we ASSUME
Note that normally the analyst would not give you
And now we divide thru by the SMALLEST molar quantity, that of oxygen, to give an empirical formula of:
And this is the empirical formula, the simplest whole number ratio defining constituent atoms in a species.
Now the molecular formula is ALWAYS a multiple of the empirical formula. That is
Thus the molecular mass must show this proportionality:
This approach is standard, however, most of the time you would not be quoted a percentage oxygen composition. You would be expected to calculate this yourself by difference.