Question

Question 15. a) What pressure in atm of gas from a scuba regulator would equal the air plus water pressure at a depth of 100 m (328 feet)?

b) What percent of a He/O₂ mix would have to be O₂ to make the partial pressure of O₂ 0.21 atm when the pressure of the mix is the value in 15.a. Show work

Answer 1

a)

We can consider the pressure exerted by air as the atmospheric pressure, that is: 1 Atm of 101325 Pa.

To this, we have to add the pressure of the 100 m of water above the subject. The pressure from a column of liquid is given by.

Where ρ is the density of the water, g is the acceleration of gravity and h is the height of water. In our case:

So the total pressure is:

b) The partial pressure of a component (in this case, O₂) in a mixture can be calculated as:

Where x_O2 is the molar fraction of O₂ in the mixture.

The pressure in Atm of the previous excercise is:

If we want to make the partial pressure of oxygen 0.21 Atm, its molar fraction has to be:

So the percentage is 1.97%.