Question

The vapour density of a mixture containing $N{O}_2$ and $N_2{O}_4$ is $27.6$. Mole fraction of $N{O}_2$ in the mixture is:

• A. $0.2$
• B. $0.4$
• C. $0.6$
• D. $0.8$

Answer 1

The correct option is D $0.8$

Let the moles of $N{O}_2$ be $x$.
So, moles of $N_2{O}_4$ will be $1-x$.
We know that, Molar mass = $2\times vapourdensity$
So, Molar mass = $2\times 27.6$ = 55.2 g
Molar mass of $N{O}_2$ = 46 g and $N_2{O}_4$ = 92 g
$\frac{x\times 46+(1-x)\times 92}{1}$ = 55.2
= $46x+92-92x=55.2$
On solving, $x=\frac{36.8}{46}=0.8$
$\therefore$ mole fraction of $N{O}_2$ will also be 0.8 and mole fraction of $N_2{O}_4$ will be 0.2.