At 298 K, you collect 0.5 L of oxygen over water that has a total pressure of 150 kPa. What is the partial pressure of oxygen? (The partial pressure of water vapor at 298 K is 3.6 kPa.)
(Points : 1)
A.) 146.4 kPa

B.) 150.4 kPa

C.) 154.6 kPa

D.) 298.6 kPa

Question

At 298 K, you collect 0.5 L of oxygen over water that has a total pressure of 150 kPa. What is the partial pressure of oxygen? (The partial pressure of water vapor at 298 K is 3.6 kPa.)
(Points : 1)
A.)       146.4 kPa

B.)       150.4 kPa

C.)       154.6 kPa

D.)       298.6 kPa

jfraser · Answer

When you collect a gas over water, a tiny amount of water $vapor$ is collected with the gas itself. The total pressure measured is from $both$ gases, not just the $O_2$. The vapor pressure of water has been measured and can be corrected for easily.

If the total pressure is made of both the $O_2$ and the water vapor, you know both the total pressure and the water vapor