Question

A sample of a breathing mixture for divers comtained 34.3% helium, 51.7% nitrogen, and 14% oxygen, by mass. What is the density of this mixture at 22degree celcius and 755mmHG?

Answer 1

If you take a 100 g sample, you will have 34.3 g He, 51.7 g N2, and 14 g O2. Convert those to moles (moles = g/molar mass), then use PV = nRT and solve for V. (n = total moles of the three gases.)
Then density = mass/volume