Question

A closed vessel contains $8 \,g$ of oxygen and $7\, g$ of nitrogen. The total pressure is $10 \,atm$ at a given temperature. If now oxygen is absorbed by introducing a suitable absorbent, the pressure of the remaining gas in atm will be

• A. 2
• B. 10
• C. 4
• D. 5

Answer 1

Answer: (D)

From Dalton's law, final pressure of the mixture of nitrogen and oxygen is
$P=P_{1}+P_{2} $
$=\frac{\mu_{1} R T}{V}+\frac{\mu_{2} R T}{V}=\frac{m_{1}}{M_{1}} \frac{R T}{V}+\frac{m_{2}}{M_{2}} \frac{R T}{V} $
$=\frac{8}{32} \frac{R T}{V}+\frac{7}{28} \frac{R T}{V}=\frac{R T}{2 V} \Rightarrow 10=\frac{R T}{2 V}$ .....(i)
When oxygen is absorbed then for nitrogen let pressure is
$P =\frac{7}{28} \frac{R T}{4 V}$
$\Rightarrow P =\frac{R T}{4 T}$ .....(ii)
From Eqs. (i) and (ii), we get pressure of the nitrogen $P=5 \,atm$