If 4.04 g of #N# combine with 11.46 g #O# to produce a compound with a molar mass of 108.0 g/mol, what is the molecular formula of this compound?

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Answer 1 · 2016-05-29T07:44:49

Dinitrogen pentoxide, #N_2O_5#.

#"Moles of nitrogen"# #=# #(4.04*g)/(14.01*g*mol^-1)# #=# #0.289*mol#

#"Moles of oxygen"# #=# #(11.46*g)/(15.999*g*mol^-1)# #=# #0.716*mol#

We divide thru by the lowest molar quantity to give an empirical formula of #NO_(2.5)# or #N_2O_5#, because the empirical formula should be integral.

Now the molecular formula is always a multiple of the the empirical formula:

So using the quoted molecular mass:

#108*g*mol^-1# #=# #nxx(2xx14.01+5xx15.999)*g*mol^-1#

Clearly, #n=1#, and the molecular formula is #N_2O_5#.