Question

A mixture of carbon monoxide and carbon dioxide is found to have a density of $1.7\text{g/L}$ at S.T.P. The mole fraction of carbon monoxide is:

• A. 0.37
• B. 0.4
• C. 0.3
• D. 0.5

Answer 1

The correct option is A 0.37

Average molecular mass, $M=\frac{dRT}{P}$
$\therefore M_{mix}=\frac{dRT}{P_{mix}}$
$M_{mix}=\frac{1.7\times 0.0821\times 273}{1}$
=$1.7\times 22.4\text{gms}$

=$38.1gmo{l}^{-1}$

Let $X_{CO}$ be the mole fraction of $CO$
Then mole fraction of $C{O}_2$ = $1-X_{CO}$
Since molar masses of $CO$ and $C{O}_2$ are $28gmo{l}^{-1}$ and $44gmo{l}^{-1}$

$M_{mix}=X_{CO}\times M_{CO}+(1-X_{CO})\times M_{C{O}_2}$
$38.1=X_{CO}\times 28+(1-X_{CO})\times 44$
$X_{CO}=0.37$