MCAT General Chemistry Question 114: Answer and Explanation

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Question: 114

9. A balloon at standard temperature and pressure contains 0.20 moles of oxygen and 0.60 moles of nitrogen. What is the partial pressure of oxygen in the balloon?

  • A. 0.20 atm
  • B. 0.25 atm
  • C. 0.33 atm
  • D. 0.80 atm

Correct Answer: B

Explanation:

At STP, the pressure inside the balloon equals 1 atm. The total number of moles in the balloon equals 0.20 moles plus 0.60 moles, or 0.80 moles. PO2 equals the mole fraction of oxygen times the total pressure, 1 atm. The partial pressure of oxygen is therefore 0.25 atm.

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