It was found that in a diving gas mixture for a certain altitude, the total predicted pressure is 8.38 atm. If the partial pressure of oxygen gas must be 0.21 atm underwater, what must the mol fraction be of oxygen gas?

1 Answer
Truong-Son N.
May 18, 2017

This is asking you to use assume O2 is an ideal gas and use the definition of partial pressure:

PO2=χO2(g)Ptot

where χO2(g) is the mol fraction of O2 in the diving gas mixture and PO2 is its partial pressure in the diving gas mixture.

Since we want PO2=0.21 atm, we have:

0.21 atm=χO2(g)(8.38 atm)

⇒χO2(g)=0.025

or 2.5%. This should make sense, since if we want only 0.21 atm of O2 at a higher pressure, we want less than 21% of the higher pressure to be O2.

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