Question

The mole percentage of oxygen in a mixture of $7g$ $N_2$ and $8g$ $O_2$ is:

• A. $25$
• B. $75$
• C. $50$
• D. $40$

Answer 1

The correct option is C $50$

Molar mass of $O_2=32g$

$8g$ of $O_2=\frac{8}{32}$ moles $=6.25$ moles.

Molar mass of $N_2=28g$

$7g$ of $O_2=\frac{7}{28}$ moles $=0.25$ moles.

Mole percentage of $O_2=\frac{Molesof{O}_2}{RatesOf(O_2+N_2)}\times 100$

$=\frac{0.25\left(100\right)}{0.25+0.25}=50$

Mole percentage of $O_2$ is $50$.