How many nitrogen atoms are in 10.2 g of copper(ii) nitrate?

To determine the number of nitrogen atoms in the given amount of a compound, we need to know the number of moles of nitrogen. In order to come to this, its is important tht we know the chemical formula of the compound which would be Cu(NO3)2 (molar mass = 187.56 g/mol). When we obtain the moles of nitrogen, we use Avogadro's number to convert the number of moles to atoms. 

Moles Cu(NO3)2 = 10.2 g Cu(NO3)2 ( 1 mol / 187.56 g ) = 0.0544 mol 
Moles N = 0.0544 mol Cu(NO3)2 ( 2 mol N / mol Cu(NO3)2 ) = 0.109 mol
Atoms N = 0.109 mol N ( 6.022 x20^23 atoms N / mol N ) = 6.55x10^22 atoms N