For divers going to great depths, the composition of the air in the tank must be modified. The ideal composition is to have approximately the same number of O2 molecules per unit volume as in surface air (to avoid oxygen poisoning), and to use helium instead of nitrogen for the remainder of the gas (to avoid nitrogen narcosis, which results from nitrogen dissolving in the bloodstream). Of the molecules in dry surface air, 78% are N2, 21% are O2, and 1% are Ar.
(a) How many O2 molecules per m 3 are there in surface air at 20.0 °C and 1.00 atm?
(b) For a diver going to a depth of 100.0 m, what percentage of the gas molecules in the tank should be O2? (Assume that the density of seawater is 1025 kg/m3 and the temperature is 20.0 °C.)