Waiting for answer This question has not been answered yet. You can hire a professional tutor to get the answer.

QUESTION

# What is the approximate molecular mass of dry air containing 78% N2 and 22% O2? Explain stepwise.

Here's one way of doing it.

You know that 1 mol of a gas occupies 22.4 L at 1 atm and 0 °C.

If that gas is air, 78 % of its volume (17.5 L) is "N"_2, and 22 % of its volume (4.9 L) is "O"_2.

The molar mass of "N"_2 is 28.0 g/mol.

If the mass of 22.4 L of "N"_2 is 28.0 g, the mass of 17.5 L of "N"_2 is

17.5 color(red)(cancel(color(black)("L N"_2))) × ("28.0 g N"_2)/(22.4 color(red)(cancel(color(black)("L N"_2)))) = "21.9 g N"_2

The molar mass of "O"_2 is 32.0 g/mol.

If the mass of 22.4 L of "O"_2 is 32.0 g, the mass of 4.9 L of "O"_2 is

4.9 color(red)(cancel(color(black)("L O"_2))) × ("32.0 g O"_2)/(22.4 color(red)(cancel(color(black)("L O"_2)))) = "7.0 g O"_2

The total mass of the two gases in 22.4 L is

m_"N₂" + m_"O₂" = "21.9 g + 7.0 g" = "28.9 g"

∴ The molar mass of dry air is 28.9 g/mol.