Question

The pressure of a mixture of equal weights of two gases of molecular weight 4 and 40 is 1.1 atm.What is the partial pressure of the lighter gas in the gas mixture?

• A. $0.55$ atm
• B. $0.75$ atm
• C. $1$ atm
• D. None of these

Answer 1

Answer: (C)

$1$ atm

According to Dalton's law of partial pressure,

$P_A={\chi }_A\times P_{\text{total}}$

where, $P_A$ = Partial pressure of gas A

${\chi }_A=$ Mole fraction of gas A

$P_{\text{Total}}=$ Total pressure

The lighter gas will have a lower value of molecular weight.

Therefore, partial pressure of lighter gas $={\chi }_{lightergas}\times P_{Total}$

$=\frac{\frac{x}{4}}{\frac{x}{4}+\frac{x}{40}}\times 1.1$

$=\frac{1\times 40\times 1.1}{4\times 11}$

$=1atm$

Hence, the correct answer is option $\text{C}$.