Question

An animal takes a breath with a volume of 1.80 L at standard temperature and pressure. If air contains a 20.9% oxygen, how many molecules of oxygen are in one breath?

Answer 1

Air inhaled$=1.80 \ L$

Oxygen inhaled$=20.9$ % of air$=\frac{20.9}{100}\times 1.80=0.3762 \ L$

Number of moles of $O_2$ in this amount$=\frac{0.3762}{22.4}=16.795\times 10^{-3} \ mol$

Number of molecules of $O_2=16.795\times10^{-3}\times 6.023 \times 10^{23}=101.156\times10^{20}$