Question

$0.157$ g of a certain gas collected over water occupies a volume of $135ml$ at ${27}^{0}C$ and $750mm$ of Hg. Assuming ideal behaviour , the molecular weight of the gas is:

(aqueous tension at ${27}^{0}C$ is $26.7mm$ of $Hg$)

• A. $30$
• B. $32$
• C. $28$
• D. $16$

Answer 1

The correct option is A $30$

Pressure of the gas= Total pressure- Aqueous tension

$\Rightarrow 750-26.7=723.3mm$ of $Hg$

$\because PV=\frac{m}{M}RT$

$\therefore \left(\frac{723.3}{760}\right)\times 135\times {10}^{-3}=\frac{0.157}{M}\times 0.0821\times 300$

$\therefore M=30$