Question

A volatile organic compound weight $0.2$ g, displaced $30$ ml of air at ${27}^{0}C$ and $756$ mm, what will be the molecular mass of the compound?

[At ${27}^{0}C$, aqueous tension is $26$ mm]

• A. $170.86$
• B. $171.95$
• C. $180.96$
• D. $189.59$

Answer 1

The correct option is A $170.86$

Mass of the substance$=0.2g$

Volume of air displaced$=30ml$

Temperature$=27°C=(27+273)K=300K$

Atmospheric pressure$=(756-26)$ mm of Hg

$=730mmHg$

Using the Ideal gas law equation,

$\frac{P_1{V}_1}{T_1}=\frac{P_2{V}_2}{T_2}$

Then volume of the displaced air at NTP$=\frac{730mm\times 30ml}{300K}\times \frac{273}{760mmHg}$

$=26.22mm$

Molecular mass$=\frac{0.2g}{26.22ml}\times 22400$$=170.86g$

Hence, option $A$ is correct.