Microanalytical data give #C, H, N: 65.73%; 15.06%; 19.21%#. What is the molecular formula if the #"vapour density=37"#?
We assume that we have been given
We get (eventually)
We find the empirical formula in the usual way; that is assume that there are
And now we divide thru by the smallest molar quantity, that of
And thus here,
As is typical, the molecular formula is a whole number multiple of the empirical formula, and thus,
The vapour density was a bit out, but in fact this persuades me that these data came from an actual experiment, and not a problem someone pulled out of their posterior. Typically, vapour density measurements are not perfect.