Question

At T (K), a gaseous mixture of H$_2$ and O$_2$ containing 20% (weight/weight) of H$_2$ exerts a total pressure of 2 bar. What is the partial pressure of O$_2$ (in bar)?

• A. 0.2
• B. 0.1
• C. 0.4
• D. 0.6

Hint:

For gas mixtures, use mole fraction to find partial pressure: $P_i = x_i \cdot P_\text{total}$.

Answer 1

The Correct Option is C

Step 1: Assume total mass of mixture = 100 g. \[ \text{Mass of H}_2 = 20\, \text{g}, \quad \text{Mass of O}_2 = 80\, \text{g} \]
Step 2: Calculate moles of each gas. \[ \text{Moles of H}_2 = \frac{20}{2} = 10 \] \[ \text{Moles of O}_2 = \frac{80}{32} = 2.5 \]
Step 3: Find mole fraction of O$_2$. \[ \text{Total moles} = 10 + 2.5 = 12.5 \] \[ \text{Mole fraction of O}_2 = \frac{2.5}{12.5} = 0.2 \]
Step 4: Find partial pressure of O$_2$. \[ P_{\text{O}_2} = \text{Mole fraction} \times \text{Total pressure} = 0.2 \times 2 = 0.4\, \text{bar} \] Final Answer: \[ \boxed{0.4\, \text{bar}} \]