Question

At a given temperature, an unknown gas takes 10.0 minutes to travel the distance helium gas travels in 1.66 minutes. What is the approximate molar mass of the unknown gas

Answer 1

Answer:

The molar mass of the unknown is approximate 145g/mol

Explanation:

We can relate the speed of effusion of gases with the molar mass of the 2 compounds using Graham´s law:

$\frac{v_a}{v_b} =\sqrt{ \frac{m_b}{m_a} }$

Where V is speed of the gas and m molar mass of a and b gases.

Molar mass of helium is 4g/mol. As the distance of the gases is the same, we can replace the speed of effusion with the time the gas takes to travel the distance. The equation will be:

$\frac{t_b}{t_a} =\sqrt{ \frac{m_b}{m_a} }$

Replacing:

$\frac{10.0min}{1.66} =\sqrt{ \frac{m_b}{4g/mol} }\\6.024 = \sqrt{ \frac{m_b}{4g/mol} }\\36.29 = \frac{m_b}{4g/mol}\\145 g/mol =m_b$

The molar mass of the unknown is approximate 145g/mol