At sea level, the atmospheric pressure is approximately 1 atm. What is the partial pressure of oxygen (O_2) in dry air at sea level?

• A. 0.03 atm
• B. 0.78 atm
• C. 0.21 atm
• D. 1.00 atm

Answer: (C)

Verified step by step guidance

1. Understand that the total atmospheric pressure at sea level is given as 1 atm.
2. Recall that dry air is a mixture of gases, primarily nitrogen (N_2), oxygen (O_2), argon (Ar), and other trace gases.
3. Identify the mole fraction of oxygen in dry air, which is approximately 0.21 (or 21%).
4. Use Dalton's Law of Partial Pressures, which states that the partial pressure of a gas in a mixture is the product of the mole fraction of that gas and the total pressure: \(P_{O_2} = X_{O_2} \times P_{total}\).
5. Calculate the partial pressure of oxygen by multiplying the mole fraction of oxygen (0.21) by the total atmospheric pressure (1 atm): \(P_{O_2} = 0.21 \times 1 \text{ atm}\).