# Microanalytical data give #C, H, N: 65.73%; 15.06%; 19.21%#. What is the molecular formula if the #"vapour density=37"#?

##### 1 Answer

We assume that we have been given

We get (eventually)

#### Explanation:

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

Now, vapour density is the density of a vapour in relation to that of dihydrogen.

And thus here,

And thus

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.

Clearly,