Question

The atmospheric pressure is $760mmHg$ at the sea level. Which of the following ranges is nearest to the partial pressure of $C{O}_2$ in mm Hg?

• A. 0.30-0.31
• B. 0.60-0.61
• C. 3.0-3.1
• D. 6.0-6.1

Answer 1

Answer: (A)

$pC{O}_2=0.30-0.31mmHg$ in air.
Air contains 0.04% of carbon dioxide.
This means that in every 100 molecules of air, 0.04 will be $C{O}_2$ molecules.
The number of moles of carbon dioxide in 100 molecules of air will be
$nC{O}_2=0.04$ molecules $\times N_A=0.04\times N_A$
The total number of moles in the sample of air will be
$n_{total}=100$ molecules $\times N_A=100N_A$
This means that mole fraction of carbon dioxide in the mixture will be
$XC{O}_2=\frac{0.04N_A}{100N_A}=0.0004$
Carbon dioxide’s partial pressure in air will thus be
$pC{O}_2=0.0004\times 760mmHg$
$=0.304mmHg$ $\therefore$ We can say it ranges between $0.30-0.31mmHg$