Helium-oxygen mixtures are used by divers to avoid the bends and are used in med

Question

Helium-oxygen mixtures are used by divers to avoid the bends and are used in medicine to treat some respiratory ailments. What percent (by moles) of He is present in a helium-oxygen mixture having a density of  0.518g/L  at 25 ?C and 721 mmHg?

Express your answer numerically as a percentage. Helium-oxygen mixtures are used by divers to avoid the bends and are used in medicine to treat some respiratory ailments. What percent (by moles) of He is present in a helium-oxygen mixture having a density of  0.518g/L  at 25 ?C and 721 mmHg?

Express your answer numerically as a percentage.

Explanation / Answer

First, reduce the density to STP.

It will be 0.518 x 300/273 x 760/721.

then density=0.600021g/l

let volume of mixture at stp be 22.4 liters

total mass=22.4*0.600021=13.440477g

at stp any ideal gas occupies 22.4 liiters of volume .so the total number of moles of mixture is 1

let number of moles of helium be H.then number of moles of oxygen will be (1-H).

so

13.440477 = 4H + 32(1-H)

13.440477=32-28H

28H=18.559523

H=0.66284

so percentage of He (in moles) present in mixture=H*100/1

=0.66284*100

=66.284%

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