Question

Given that a sample of air is made up of nitrogen, oxygen, and argon in the mole fractions 78% N2, 21% O2, and 1.0% Ar, what is the density of air at standard temperature and pressure?

Answer 1

you take density of each molecule and multiply it with ratio:
rho = 0,78 * 1.251 g/L + 0,21 * 1.429 g/L + 0,01 * 1,784 g/L
rho = 1,294 g/L