Question

Equal masses of methane and oxygen are mixed in an empty container at $25^??$. The fraction of the total pressure exerted by oxygen is

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

Answer 1

Answer: (C)

$\frac{1}{3}$

Answer 2

Let the mass of methane and oxygen is $w$ mole fraction of oxygen $=\frac{\frac{w}{32}}{\frac{w}{32}+\frac{w}{16}}$ $=\frac{\frac{1}{32}}{\frac{1}{32}+\frac{1}{16}}=\frac{\frac{1}{32}}{\frac{3}{32}}=\frac{1}{3}$ Let the total pressure be $P$ The pressure exerted by oxygen (partial pressure) $=X_{O_2}\times P_{total}$ $\Rightarrow P\times\frac{1}{3}$ Hence, (3) is correct.