# What are the mole fraction and the mole percent of oxygen in exhaled air if P (subscript of O2) is 116 torr and a P (subscript of total) is 788 torr? I not sure if the question makes sense.

Mar 25, 2015

The mole fraction of oxygen in exhaled air is $\text{0.147}$, and the mole percent is $\text{14.7%}$.

You were given the total pressure of an air sample and the partial pressure of oxygen, which means that you can solve for the mole fraction of oxygen by using

${P}_{\text{oxygen") = chi_("oxygen") * P_("total}}$, where

${\chi}_{\text{oxygen}}$ - the mole fraction of oxygen.

${P}_{\text{oxygen") = chi_("oxygen") * P_("total") => chi_("oxygen") = P_("oxygen")/P_("total}}$

chi_("oxygen") = (116cancel("torr"))/(788cancel("torrr")) = "0.147"

The mole percent is imply the mole fraction multiplied by 100, so

$\text{mole%" = chi_("oxygen") * 100 = "0.147" * 100 = "14.7%}$