# Problem: 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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###### FREE Expert Solution

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 = ?

###### Problem Details

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.