Question

To prevent a condition called the “bends”, deep sea divers breathe a mixture containing, in mole percent, 10.0% O2, 10.0% N2 , and 80.0% He.. a.Calculate the molar mass of this mixture.. b.What is the ratio of the density of this gas to that of pure Oxygen?

Answer 1

The molar mass of the mixture is the summation of the molar mass of a compound in a mixture to its respective molar mass. In this case, 0.10*32 g/mol added to 0.10*28 g/mol and 0.80 *4 g/mol is equal to 9.2 g/mol. The density ratio of the gas to pure oxygen is the ratio of the molar mass between the two, hence 9.2/32 is 0.2875. 

Answer 2

Molar mass = 0.1 * MO2 + 0.1 * MN2 + 0.8 * MHe
molar mass = 9.2 g / mo

For the second part, use PV=nRT, arranged for density. The density ratio of the gas to pure oxygen is the ratio of the molar mass between the two

ratio = PM / RT

ratio = 9.2 / 32 

ratio = 0.2875