We will assume that the question is discussing 1.000 atm of N₂ initially. The question is discussing diffusion rates of two gases and asks us to identify the species. We can use Graham's Law to attempt this problem with the following formula:
Rate₁/Rate₂ = sqrt(M₂/M₁)
We are told that the N₂ is 3.55 times as fast as the unknown species, so rate 1 = 3.55 and rate 2 = 1. We know the molecular weight of N₂ as 28 g/mol. Now we can use the equation above to solve for the molecular weight of the unknown, M₂:
3.55/1 = sqrt(M2/28)
(3.55)² = M₂/28
M₂ = 28 (3.55)₂
M₂ = 353 g/mol
The unknown compound has a molecular mass of roughly 353 g/mol and this is very close to the molecular mass of UF₆ which is 352.02 g/mol. Therefore, it is likely that the unknown gas is UF₆.
