Graham's law question

Question

Under identical conditions, separate samples of O₂ and an unknown gas were allowed to effuse through identical membranes simultaneously. After a certain amount of time, it was found that 6.316.31 mL of O₂ had passed through the membrane, but only 3.123.12 mL of the unknown gas had passed through.

What is the molar mass of the unknown gas?

unknown molar mass:

g/mol

Answer 1

Graham's Law of Effusion:

rate gas 1 / rate gas 2 = sqrt MW gas 2 / sqrt MW gas 1

gas 1 = O2; molar mass = 32 g/mol

gas 2 = unknown; molar mass = x

6.31 / 3.12 = sqrt x / sq rt 32

2.022 = sqrt x / 5.659

sqrt x = 11.438

x = 130.8 g/mol = molar mass of unknown