Question

$\text{100} \, \text{ml}$ of $O_{2}\left(g\right)$ effuse from a porous container in $\text{100} \, \text{sec} \text{.}$ $\text{75} \, \text{ml}$ of unknown gas effuses under the same conditions of temperature and pressure in $\text{150} \, \text{sec} \text{.}$ Calculate vapour density of unknown gas?

• A. 16
• B. 32
• C. 64
• D. 128

Answer 1

Answer: (C)

$\frac{r_{o_{2}}}{r_{\text {unknown }}}=\frac{\frac{v_{1}}{t_{1}}}{\frac{v_{2}}{t_{2}}}=\sqrt{\frac{M_{\text {unknown }}}{M_{o_{2}}}}$
$\Rightarrow \frac{100 \times 150}{100 \times 75}=\sqrt{\frac{ M _{\text {unknown }}}{32}}$
$\Rightarrow M _{\text {unknown }}=128$
$\therefore $ V.D. $=\frac{128}{2}=64$