Question

Equal masses of helium and oxygen are mixed in a container at ${25}^{\circ }C$. The fraction of the total pressure exerted by oxygen in the mixture of gases is :

• A. $1/3$
• B. $2/3$
• C. $1/9$
• D. $4/9$

Answer 1

The correct option is C $1/9$

Mole fraction of $O_2=\frac{\frac{w}{32}}{\frac{w}{32}+\frac{w}{4}}=\frac{w}{32}\times \frac{32}{9w}=\frac{1}{9}$
Partial pressure of oxygen $=P\times x_{O_2}$
$=P_{total}\times \frac{1}{9}$ or $\frac{1}{9}{P}_{total}$.