States of Matter - Result Question 74
74. An evacuated glass vessel weighs $50.0 \hspace {1mm} g$ when empty $148.0 g$ when filled with a liquid of density $0.98 \hspace {1mm} g \hspace {1mm} mL^{-1}$ and $50.5 g$ when filled with an ideal gas at $760 \hspace {1mm} mm \hspace {1mm} Hg$ at $300 \hspace {1mm} K$. Determine the molar mass of the gas.
(1998, 3M)
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Answer:
Correct Answer: 74. $(123 {~g}{~mol}^{-1})$
Solution:
Mass of liquid $=148-50=98 \hspace {1mm} g$
$\Rightarrow$ Volume of liquid $=\dfrac{98}{0.98}=100 \hspace {1mm} mL=$ volume of flask
mass of gas $=50.5-50=0.50 g$
Now applying ideal gas equation : $p V=\left(\dfrac{w}{M}\right) R T$
$\Rightarrow \quad M=\dfrac{w R T}{p V}=\dfrac{0.5 \times 0.082 \times 300}{1 \times 0.1}=123 {~g} {~mol}^{-1}$
BETA
