# Question f9291

Aug 20, 2017

The mole percentage of ${\text{N}}_{2}$ is 75 %.

#### Explanation:

Assume that you have 1 mol of air.

Let $x$ be the mole fraction of ${\text{N}}_{2}$.

Then $1 - x$ is the mole fraction of ${\text{O}}_{2}$

Then average atomic mass of air is given by

"Mole fraction of N"_2 × M_text(r, N₂) + "Mole fraction of O"_2 × M_text(r, O₂) = 29

x × 28.01 + (1-x) × 32.00 = 29

$28.01 x + 32.00 - 32.00 x = 29$

$3.99 x = 32.00 - 29 = 3$

$x = \frac{3}{3.99} = 0.75$

"Mole percent" = "mole fraction × 100 %" = 0.75 × 100 % = 75 %#