Q. On a humid day in summer, the mole fraction of gaseous a $H_{2}O$ (water vapour) in the air at $25^{\circ}C\$ can be as high as 0.0287. Assuming a total pressure of 0.977 atm. What is the partial pressure of dry air?
A) 94.9 atm
B) 0.949 atm
C) 949 atm
D) 0.648 atm
Explanation
(b)
$P_{H_{2}O} =$ $X_{H_{2}O}\ p_{total}\$
$\ \ \ \ \ \ \ \ \ \ = 0.0287 \times 0.977$
=0.028atm
$p_{total}\$= $p_{dry\ air} + p_{H_{2}O}\$
$p_{dry\ air} = p_{total} + p_{H_{2}O}$
= 0.977-0.028 =0.949 atm
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.