A compound composed of 2.1% H, 29.8% N, and 68.1% O has a molar mass of approximately 50 g/mol. What is the formal charge of the nitrogen?

1 Answer
Aug 15, 2016

Answer:

Nitrogen has a ZERO formal charge in nitrous acid, #HNO_2#

Explanation:

We need (i) to obtain the emprical, and (ii) the molecular formula of the nitrogen species:

If we assume 100 g of stuff, there are,

#H: # #(2.1*g)/(1.008*g*mol^-1# #=# #2.08" moles of hydrogen"#

#N: # #(29.8*g)/(14.01*g*mol^-1# #=# #2.13" moles of nitrogen"#

#O: # #(68.1*g)/(16.0*g*mol^-1# #=# #4.26" moles of oxygen"#

We divide thru by the lowest molar quantity to give #HNO_2# as the empirical formula, the simplest whole number ratio that defines constituent elements in a species.

But we know that the chemical formula is ALWAYS a mulitple of the empirical formula:

And thus, #50.0*g*mol^-1# #~=# #(1.008+14.01+2xx16.0)*g*mol^-1xxn#

In nitrous acid, the charge on #N# is formally zero; it has the 5 valence electrons, with which the 2 inner core electrons, balance the nuclear charge of #+7#. In nitric acid, #HNO_3#, nitrogen would be quaternized and carry a formal #+1# charge.