Density of dry air containing only N2 and O2 is 1.15 g/L at 740 mm of Hg and 300 K. What is % composition of N, by weight in the air ?

d=PMRT1.15=740760×M0.0821×300∴ M=29.09. Let mole fraction of N2 is x.29.09=28×x+32(1−x);x=0.7275 wt. %= mole %× mol.wt.of N2 average mol.wt.ofair =72.75×2829.09=70.02