The volume occupied by 3.2 g of oxygen at STP is:
Correct answer: B. 2.24 dm3
- A. 22.4 dm3
- B. 2.24 dm3
- C. 11.2 dm3
- D. 16.0 dm3
Explanation
At STP, one mole of any ideal gas occupies 22.4 dm3. The molar mass of oxygen (O2) is 32 g/mol. Therefore, the number of moles in 3.2 g of oxygen is 3.2 g / 32 g/mol = 0.1 moles. The volume occupied by 0.1 moles of oxygen is 0.1 × 22.4 dm3 = 2.24 dm3.Option A represents the full molar volume at STP, not applicable to 3.2 g. Option C is half the molar volume, applicable to 16 g of oxygen, not 3.2 g. Option D does not correlate with any significant fraction of molar volume in this context.
This question appeared on the ETEA MDCAT 2012 paper, which you can sit online with every answer explained.
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About Standard Temperature and Pressure
Standard temperature and pressure provide reference conditions for gas calculations: 0°C or 273 K and, in the usual school convention, 1 atm pressure. Questions use these conditions to relate pressure, volume, temperature and amount of gas, including the molar volume of an ideal gas, about 22.4 dm³.
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