Molar mass and density?

Question

Dry air (0% humidity) is approximately 78% N2, 21% O2, and 1% Ar by moles. Calculate the molar mass and density of dry air at 0 °C and 1.0 atm. Assume ideal behavior and use two significant figures in your answers.

20673 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2016-11-19T04:27:34

Molar masses of constituent elements and their corresponding number of moles in air

$"Element"" ""molar mass"" "" "" "mol%$

$" "N_2" "" "28.013" g/mol"" "" "78%$

$" "O_2" "" "31.998" g/mol"" "" "21%$

$" "Ar" "" "39.948" g/mol"" "" "01%$

Taking weighted average the molar mass of air is

$M_"air"->(78xx28.013+21xx31.998+1xx39.948)/100~~28.969" g/mol"$

At STP Molar volume is $22.4"mol/L"$

$"So density of air at STP "="molar mss"/"molar volume"$

$=(28.969g/"mol")/(22.4L/"mol")~~1.293g/L$