Question

Equal masses of methane and oxygen are mixed in an empty container at ${25}^{\circ }C$. The fraction of the total pressure exerted by oxygen will be:

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

Answer 1

Answer: (D)

$\frac{1}{3}$

Let $32gmC{H}_4$ and $O_2$ each are mixed and let total pressure be $P$.
Moles of $C{H}_4=\frac{32}{16}=2moles$
Moles of $O_2=\frac{32}{32}=1mole$
${\chi }_{C{H}_4}=\frac{2}{3}$
${\chi }_{O_2}=\frac{1}{3}$
According to Dalton's law of partial pressure,
$P_A={\chi }_A.P_{total}$
$P_{O_2}=\frac{1}{3}\times P=\frac{P}{3}$
$\therefore O_2$ exerts one - third of total pressure.