Question

A gas mixture contains an equal number of molecules of $N_2$ and $S{F}_6$, some of it is passed through a gaseous effusion apparatus. Calculate how many molecules of $N_2$ are present in the product gas for every 100 molecules of $S{F}_6$.
Write your answer to the nearest integer.

Answer 1

The rate of effusion is inversely proportional to the molar mass.

$\frac{r_{N_2}}{r_{S{F}_6}}=\sqrt{\frac{M_{S{F}_6}}{M_{N_2}}}=\sqrt{\frac{146}{28}}=2.28$

Hence, for every 100 molecules of $S{F}_6$, the number of nitrogen molecules present is $100\times 2.28=228$ molecules.