Question

Equal weights of methane and oxygen are mixed in an empty container at ${25}^{o}C$. The fraction of the total pressure exerted by oxygen is:

• A. $\frac{1}{3}$
• B. $\frac{1}{2}$
• C. $\frac{2}{3}$
• D. $\frac{1}{3}\times \frac{273}{298}$

Answer 1

The correct option is A $\frac{1}{3}$

Let $xg$ each of oxygen and methane are mixed.
The moles of oxygen and methane are $\frac{x}{32}$ and $\frac{x}{16}$ respectively.
The mole fraction of oxygen is $=\frac{\frac{x}{32}}{\frac{x}{32}+\frac{x}{16}}=\frac{1}{3}$.
The partial pressure of oxygen is the product of its mole fraction and total pressure.
Thus $P{O}_2=p\times \frac{1}{3}$ or $\frac{P{O}_2}{p}=\frac{1}{3}$.