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. $\frac{1}{4}$

Answer 1

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

The molar masses of methane and oxygen are 16 g/mol and 32 g/mol.
Assume 16 g of methane are mixed with 16 g of oxygen.
Hence, 1 mole of methane is mixed with 0.5 mole of oxygen.
The mole fraction of oxygen is $\frac{0.5}{1+0.5}=\frac{1}{3}$.
This is equal to the fraction of total pressure exerted by oxygen.