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. $=\frac{128}{2}=64$