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).

= 146.4 kPa
Dalton's law of partial pressures states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases.
Total pressure = Pgas 1 +Pgas 2+Pgas 3 + .........
Therefore;
Partial pressure of Oxygen = Total pressure - partial pressure of water vapor
= 150kPa - 3.6 kPa
= 146.4 kPa