Recall: Graham's Law of Effusion allows us to compare the rate of effusion of two gases. Graham's Law states that the rate of effusion of a gas is inversely proportional to its molar mass.
This means that when comparing two gases:
Let's designate HBr as gas 1 and the unknown as gas 2. We're given:
rateHBr = 15.0 mL/min MHBr = 1.01 g/mol H + 79.90 g/mol Br = 80.91 g/mol
rateunk = 20.3 mL/min Munk = ?
In a given diffusion apparatus, 15.0 mL of HBr gas diffuses in 1.0 min. In the same apparatus and under the same conditions, 20.3 mL of an unknown gas diffuses in 1.0 min. The unknown gas is a hydrocarbon.
Find its molecular formula.
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