Answer to Question #96640 in General Chemistry for Angel

Question

A sample of an unknown gas effuses in 12.6 min. An equal volume of N2 in the same apparatus at the same temperature and pressure effuses in 7.0 min. What is the molar mass of the unknown gas?

Answer 1

By using Graham law of diffusion or effusion:

$\frac{t_2}{t_1}=\sqrt{\frac{m_2}{m_1}}$ ;

where $t_1$ and $t_2$ are the time required for effusion of gases and $m_1$ and $m_2$ are molecular mass of gases.

$t_2=12.6\ min$ ;

$t_1=7 \ min$;

$m_1=14\times 2=28\ gm$ ;

Using the above equation:

$\frac{12.6}{7}=\sqrt{\frac{m_2}{28}}$ ;

$m_2=90.72 \ gm$ (mass of unknown gas)