Human lungs have evolved to breathe oxygen at a pressure as that in the atmosphere, 0.21 atm. If a particular heliox mixture to be carried by a scuba diver is at a pressure of 7.00 atm, what should be the partial pressure due to helium in order to maintain the pressure due to oxygen at 0.21 atm?

6.79 atm

Explanation:

Applying Dalton's law of partial pressure:

, where = total partial pressure of all the component gases in the mixture, = partial pressure of helium gas, and = partial pressure of oxygen gas.

From the illustration, = 7.00 atm and = 0.21 atm. Hence, the partial pressure due to helium is calculated such that:

=

           = 7.00 - 0.21

              = 6.79 atm

Therefore, the partial pressure due to helium in order to maintain the pressure due to oxygen at 0.21 atm would be 6.79 atm.

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