A sample of \(\mathrm{N}_{2}(\mathrm{g})\) effuses through a tiny hole in \(38 \mathrm{s}\) What must be the molar mass of a gas that requires \(64 \mathrm{s}\) to effuse under identical conditions?

Short Answer

Expert verified
The molar mass of the unknown gas, that effuses in 64 seconds under the same conditions as nitrogen, is about 47.3 g/mol.

Step by step solution

01

Understanding Graham's law of effusion

Graham’s law of effusion states that, under the same conditions of temperature and pressure, the rate of effusion of different gases is inversely proportional to the square root of their molar masses. Mathematically this can be written as: \( r_1 / r_2 = \sqrt {M_2 / M_1} \) where r is the rate of effusion and M is the molar mass.
02

Apply the rates and molar mass given

Here, the rate of effusion is proportional to 1/time required. So we can express \( r_1 = 1/t_1 \) and \( r_2 = 1/t_2 \). Given in the problem, \( r_1 = 1/38s \) and \( r_2 = 1/64s \). The first gas is nitrogen with a molar mass \( M_1 = 28 g/mol \). Substituting these into Graham’s law equation we get: \( (1/38s) / (1/64s) = \sqrt {M_2 / 28 g/mol} \)
03

Solve the equation

Rearranging to solve for \( M_2 \), we get: \( M_2 = [(64/38)^2] * 28 g/mol \). Solving this, we get \( M_2 = 47.3 g/mol \). So the molar mass of the unknown gas is about 47.3 g/mol.

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