Question

Density of air containing only N₂ and O₂ is 1.146 g/l  and 700 mm and 300 Kelvin.what is the percentage composition of and N₂ by weight in the air.

Answer 1

PV = n RT= (m/M) RT

M= dRT /P

=1.15 x .0821 x 300/ 700 /760 = 30.75gmol^-1

Let w1 be the mass fraction of N2 ans 1- w2 is the mass fraction of O₂

so w₁ X28 + (1- w₁ )X 32 = 30.75

w₁ = 0.3125

% compostion of N₂ = 31.25 %

% composition of O₂ = 68.75 %