Question

A volatile organic compound weighing $0.2$ g, on heating in Victor Meyer's tube, displaced $30$ mL of air at ${27}^{0}C$ and $756$ mm atmospheric pressure. Determine the molecular mass of the compound (Aqueous tension at ${27}^{0}C=26$ mm).

• A. $180.2$
• B. $200.5$
• C. $199.1$
• D. $190.6$

Answer 1

The correct option is C $199.1$

Mass of the substance taken = 0.2 g

Volume of air displaced = 30 mL

Temperature $={27}^{\circ }C=(27+273)K=300K$

Atmospheric pressure = (756 - 26) mm Hg = 730 mm Hg

Then,

Volume of displaced air at NTP $=\frac{730mmHg\ast 30mL}{300K}\ast \frac{273K}{760mmHg}$

$=2.5mL$

Therefore, Volume of the vapours at NTP = 22.5 mL

Then,

Molecular Mass $=\frac{Massofthecompound}{VolumeofvaporsatNTP\left(inmL\right)}\ast 22400$

$=\frac{0.2\ast 22400}{22.5}=199.1$