# How many molecules are there in 122 grams of NO_2?

Nov 14, 2015

Molecular mass of nitric oxide is $46.1$ $g$. So number of molecules $=$ $\frac{122 \cdot g}{46.1 \cdot g} \times {N}_{A}$. ${N}_{A}$ is Avogadro's number.

#### Explanation:

Avogadro's number, ${N}_{A}$ $=$ $6.02214$ $\times$ ${10}^{23}$. It is a fact that if I have Avogadro's number of hydrogen atoms (i.e. ""^1H atoms) I have a $1$ $g$ mass precisely. So your answer is $\frac{122 \cdot g}{46.1 \cdot g} \times {N}_{A}$ molecules (pretty large but not infinite). If I asked for the number of nitrogen atoms how many would I have? If I asked for the number of oxygen atoms how many would I have? And what if I asked for the total number of atoms?