Question

On a humid day in summer, the mole fraction of gaseous $H_{2}O$ (water vapour) in the air at ${25}^0$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

Answer 1

Answer: (B)

$0.949$ atm

$p_{H_{2}O}=X_{H_{2}O}{p}_{\text{total}}$

$=0.0287\times 0.977=0.028atm$

$p_{\text{total}}=p_{\text{dryair}}+p_{H_{2}O}$

$p_{\text{dryair}}=p_{\text{total}}-p_{H_{2}O}=0.977-0.028=0.949atm$