The density of a gas is 1.964 g dm-3 at 273 K and 76 cm Hg. The gas is _________?
Correct answer: B. CO2
- A. CH4
- B. CO2
- C. C2H4
- D. Xe
Explanation
At 273 K and 76 cm Hg, the gas is at STP, where one mole occupies about 22.4 dm3. Its molar mass is density x molar volume = 1.964 g dm-3 x 22.4 dm3 mol-1 = 43.99 g mol-1, which matches CO2 at about 44.0 g mol-1. Students may choose Xe because it is also heavy, but xenon has a molar mass of about 131.3 g mol-1.
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About Ideal Gas Equation
The ideal gas equation, PV = nRT, relates pressure, volume, amount and absolute temperature when gas particles are assumed to have negligible volume and no intermolecular forces. Applications include finding molar mass, density or an unknown gas variable, with careful use of Kelvin temperature and consistent units, and comparison with real-gas behaviour.
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