in oder to find the mass of one molecule of ##NO_2## nitrogen dioxide, which could actually be the polyatomic ion nitrite ##NO_2^-1##, we must convert one molecule to moles and than moles to grams.

molecules ##->## moles ##->## grams

Begin with one molecule and convert it to moles by using Avogadro’s number ##6.02 x 10^23##

1 molecule ##NO_2## x ##((1 mol)/(6.02 x 10^23))## = ##1.66 x 10^-24## moles

Now convert the moles to grams by using the molar mass (gfm) of ##NO_2##

N = 14.01 x 1 = 14.01 g ##O_2## = 16.0 x 2 = 32.0 g 14.01 + 32.0 = 46.01 g

##1.66 x 10^-24## moles x ##((46.01 g)/(1 mol))## = ##7.64 x 10^-23## grams ##NO_2##