Question

Deduce the number of nitrogen atoms in:

5.00 x 10^-3 mol of ammonia, NH3

and

4.601 g of nitrogen dioxide, NO2

Answer 1

There are 6.02E23 molecules in 1 mol.
In 5.00E-3 mols NH3 there are 5.00E-3 x 6.02E23 molecules = approx 3E21.
Then there is 1 N atom in 1 molecule of NH3; therefore, there must be about 3E21 atoms N. If your prof is picky about significant figures you need to make the answer consistent with those rules.

The second one is done the same way.

Answer 2

So, you don't have to do anything about the H3 or the O2?

Answer 3

Yes and no. First, the problem asks about N and not H. You do use H in determining the molar mass NH3 which is 14 for N and 3*1 = 3 for H to make 17 for NH3. Since you know the number of atoms of N, however, it is easy to calculate the number of atoms of H in NH3. It's just 3x that.

Answer 4

Thank you for the help!