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
May 18, 2017

This is asking you to use assume "O"_2 is an ideal gas and use the definition of partial pressure:

P_(O_2) = chi_(O_2(g))P_(t ot)

where chi_(O_2(g)) is the mol fraction of "O"_2 in the diving gas mixture and P_(O_2) is its partial pressure in the diving gas mixture.

Since we want P_(O_2) = "0.21 atm", we have:

"0.21 atm" = chi_(O_2(g))("8.38 atm")

=> color(blue)(chi_(O_2(g)) = 0.025)

or 2.5%. This should make sense, since if we want only "0.21 atm" of "O"_2 at a higher pressure, we want less than 21% of the higher pressure to be "O"_2.