Question

Air contains $79$% $N_2$ and $21$% $O_2$ by volume. If the barometric pressure is $750mm$ $Hg$ the partial pressure of oxygen is:
($d{N}_2=1.25,d{O}_2=1.42g/m$)

• A. $175.5mm$ of $Hg$
• B. $157.5mm$ of $Hg$
• C. $315.0mm$ of $Hg$
• D. None

Answer 1

Answer: (B)

The correct option is A $157.5mm$ of $Hg$

You can easily calculate the partial pressure of oxygen keeping in mind the definition of partial pressure.

First of all You have the find out the mole fraction of the oxygen and we know that mole fraction can be calculated from percentage composition of the gas divided by the total percentage of all gases

So here oxygen is 21% = mole fraction of 21 % oxygen $=\frac{21}{100}=0.21$

Here total pressure is give which is $=750$ mm of $Hg$

Partial pressure of oxygen will be $=750\times 0.21=157.5mmofHg$.

So partial pressure of oxygen will be $157.5mmHg$