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The density of an unknown gas under STP conditions is 3.17 g.L-1. What is the molecular mass of the gas?
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Correct Answer: D. 3.17 x 22.4 = 71.0
STP is Standard Temperature and Pressure or 0oC and 1 atm pressure. At STP 1 mole of an ideal gas occupies 22.4 L. A good approximation of the molecular mass of a gas is obtained by multiplying its density in g.L-1 by 22.4 L to attain the mass of 1 mole of gas. Hence: 3.17 x 22.4 = 71.0
24.5 L is the molar volume of an ideal gas under LTP or Laboratory Temperature and Pressure, a balmy 25oC and 1 atm pressure.
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