Answer – We are given, percent of N2
in air = 80.00 %
For O2 = 20.00 % , P = 1.00 atm , T = 25 +273 = 298
K
We need to calculate the mass of N2 and
O2
mass of N2 = 28.014*80.0 % / 100 %
          Â
      = 22.41 g
Mass of O2 = 31.998 g * 20.0 % / 100 %
                  Â
= 6.399 g
So total mass of air = 22.41 +6.399
                             Â
= 28.81 g
We know formula for calculating the density
Density = PM/RT
            Â
= 1.00 atm * 28.81 g / 0.0821 atm.L.mol-1.K-1
* 298 K
            Â
= 1.18 g/L
The density of air is 1.18 g/L
