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**Pressure Problem!!**

## Homework Statement

Oxygen at pressures much greater

than 1 atm is toxic to lung cells. By weight, what ratio of

helium gas (He) to oxygen gas (O2 ) must be used by a

scuba diver who is to descend to an ocean depth of

50.0 m?

## Homework Equations

## The Attempt at a Solution

I first found the total pressure at that depth (note they didn't explicity give me rho_seawater, but I assumed):

P_50m = pgh = (1020kg/m^3)g(50m) = 4.93atm. Now here's where I get stuck. I assume that since O2 can only be 1atm, thus Helium must take up 4.93atm - 1atm = 3.93atm. Then I put these back into their own P = pgh, and solve for their 'p':

1atm =(p_O2)gh -> p_O2 = 206.7kg/m^3. Doing the same thing for p_He, I get 812.5kg/m^3. Then I simply take the ratio, and get phe/po2 = 3.93. The answer says 0.625. Any ideas??

Ari