A compound that contains only nitrogen and oxygen is 30.4% N by mass; the molar mass of the compound is 92 g/mol. What is the empirical formula and the molecular formula of the compound?

1 Answer
Nov 9, 2015

Answer:

Empirical formula is #NO_2#, and the molecular formula is #N_2O_4#, dinitrogen tetroxide.

Explanation:

In #100* g# of this compounds there are #30.4* g# #N#, and the balance #O#. We divide thru by the atomic masses in order to approach the empirical formula: #(30.4*g)/(14.01*g*mol^-1)# #=# #2.17*mol*N#;

#(69.6*g)/(16.0*g*mol^-1)# #=# #4.35*mol*O#.

After we divide thru by 2.17, we get an empirical formula of #NO_2#. And as I (and many others) have said before, the empirical formula #"is the simplest whole number ratio defining constituent atoms"#
#"in a species."#

Now the molecular formula is always a multiple of the empirical formula; i.e. #MF = (EF)_n#, or #92.4*g*mol^-1# #=# #2xx(14.01 + 2 xx 16.00)(g*mol^-1)#. So #n# #=# #2#, and the molecular formula is #N_2O_4#, i.e. dinitrogen tetroxide. the dimer of #NO_2# radical.