A fixed volume of pure $N X_{2}$ (molar mass 28) effuses through a pinhole in $60.0 s$ . The same volume of a mixture of $N X_{2}$ and $O X_{2}$ (molar mass 32) effuses in $63.0 s$ under identical conditions. Treating the mixture as a single gas of average molar mass, the mole percent of $O X_{2}$ in the mixture (two decimals) is

Numerical answer type, answer in %, tolerance 0.05.

Answer: 71.75 %

t \propto M

for equal volumes, so

\overset{ˉ}{M} = 28 \times (\frac{63.0}{60.0})^{2} = 30.870 g mo l^{- 1}

. With

x

the mole fraction of

O X_{2}

28 + 4 x = 30.870

x = 0.7175

, i.e.

71.75

mole percent.