Question

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

Answer 1

Answer: (C)

$\frac{1}{3}$

The molar masses of methane and oxygen are 16 g/mol and 32 g/mol respectively.
Assume 32 g of methane are mixed with 32 g of oxygen.
The number of moles of methane and oxygen are $\frac{32}{16}=2$ moles and $\frac{32}{32}=1$ mole respectively.
The mole fraction of oxygen is $\frac{1}{1+2}=\frac{1}{3}$. it is also equal to the fraction of the total pressure exerted by oxygen.