A sample of Oxygen effuses through a porous container about 2 times faster than an unknown gas. Estimate the molar mass of the unknown gas.

The molar mass of the unknown gas is 128g/mol

Explanation:

The rate of effusion of 2 different gases follows the equation:

Rate gas A / Rate gas B = √MM gas B / √MM gas A

Where rate is the speed of effusion of each gas and MM the molar mass of each gas

If gas A is oxygen and gas B the unknown:

Rate gas A / Rate gas B = 2 = √MM gas B / √32g/mol

11.134 = √MM gas B

128g/mol = MM gas B

The molar mass of the unknown gas is 128g/mol

the answer for sodium is 0.186

the answer for rubidium is 0.251