Question

Density of air containing only N2 and O2 is 1.146 g/l and 700mm 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 %