Question

Analysis of a compound shows that it contains 7.0 g nitrogen and 16.0 g oxygen. What is its empirical formula?

Answer 1

`NO_2`

Explanation:

The empirical formula is the simplest whole number that defines constituent atoms in a species.

Using the given masses, and the atomic masses of each constituent, we define an empirical formula this way:

`"Moles of nitrogen"` `=` `(7.0*g)/(7.0*g+16*g)xx1/(14.01*g*mol^-1)=0.0217*mol`.

`"Moles of oxygen"` `=` `(16.0*g)/(7.0*g+16*g)xx1/(15.999*g*mol^-1)=0.0435*mol`.

And thus we have the molar quantities of nitrogen, and oxygen respectively. To access the empirical formula, we simply divide thru by the LOWEST molar quantity, that of nitrogen:

`N:(0.0217*mol)/(0.0217*mol)=1`

`O:(0.0435*mol)/(0.0217*mol)=2`

And thus the empirical formula is `NO_2`.

Note that to find the molecular formula we need an estimate of molecular mass.