Question

The vapour density of a mixture containing $N{O}_2$ and $N_2{O}_4$ is $28.75$ at ${27}^o\text{C}$. Calculate the moles of $N{O}_2$ in $100\text{g}$ of the mixture.

• A. $1.30$
• B. $2.30$
• C. $3.30$
• D. $4.30$

Answer 1

The correct option is A $1.30$

We know,
$\text{Molar mass}=2\times \text{Vapour density}$
$\text{Molar mass of mixture}=2\times 28.75=57.5$
$\text{Number of moles in 100 g of mixture}=\frac{100}{57.5}$
$\text{Let}a\text{g of}N{O}_2\text{is present in mixture}$.
$\text{Moles of}N{O}_2+\text{Moles of}{N}_2{O}_4=\text{Moles of mixture}$
$\frac{a}{46}+\frac{100-a}{92}=\frac{100}{57.5}\Rightarrow 100+a=\frac{100\times 92}{57.5}\Rightarrow a=60\text{g}$
$\text{Moles of}N{O}_2\text{in mixture}=\frac{60}{46}=1.30$