Question

Density of dry air (only $N_2\&O_2$) is 1.146g litre at 740mm and 300K. Calculate composition of air by weight assuming ideal nature:

Answer 1

$PM=dRT$

$\Rightarrow \frac{740}{760}\times M=1.146\times 0.082\times 300$

$\Rightarrow M=\frac{1.146\times 8.2\times 3\times 38}{37}$

$\Rightarrow x\times M_1=28.59+(1-x)M_2$

$\Rightarrow x\times 28+(1-x)32=28.59$

$\Rightarrow 32-4x=28.5x$

$\Rightarrow x=+\frac{3.04}{4}\times 0.76$

$\therefore O_2\to 1-x=0.24$ by mol in $1$ molcur

$\therefore$ by weight $N_2:O_2=\frac{0.76\times 28}{0.24\times 32}$

$=133:48$