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.

1 Answer
Stefan V.
Mar 25, 2015

The mole fraction of oxygen in exhaled air is #"0.147"#, and the mole percent is #"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_("oxygen") = chi_("oxygen") * P_("total")#, where

#chi_("oxygen")# - the mole fraction of oxygen.

In your case, you'll get

#P_("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

#"mole%" = chi_("oxygen") * 100 = "0.147" * 100 = "14.7%"#

Read more about mole fraction and mole percent here

http://socratic.org/questions/what-is-mole-percent

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