Question

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.

Answer 1

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