NLN NEX Chemistry Practice Test

A gas sample at STP has a mass of 44.0 g and occupies 11.2 L. What is its molar mass?

44.0 g/mol 22.4 g/mol 66.0 g/mol 88.0 g/mol

Correct Answer:

88.0 g/mol

Explanation:

At STP, one mole of any gas occupies 22.4 liters. The amount of gas here is n = 11.2 L ÷ 22.4 L/mol = 0.5 mol. Molar mass is mass per mole, so M = 44.0 g ÷ 0.5 mol = 88.0 g/mol. So the molar mass is 88.0 g/mol. (Half a mole has 44.0 g, so a full mole would weigh 88.0 g.)

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