Molar mass and density?

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Molar mass and density?

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.

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Answer 1 · 2016-11-19T04:27:34

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

$Element molar mass m o l %$ $"Element"" ""molar mass"" "" "" "mol%$

$N_{2} 28.013 g/mol 78 %$ $" "N_2" "" "28.013" g/mol"" "" "78%$

$O_{2} 31.998 g/mol 21 %$ $" "O_2" "" "31.998" g/mol"" "" "21%$

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

Taking weighted average the molar mass of air is

$M_{air} \to \frac{78 \times 28.013 + 21 \times 31.998 + 1 \times 39.948}{100} \approx 28.969 g/mol$ $M_"air"->(78xx28.013+21xx31.998+1xx39.948)/100~~28.969" g/mol"$

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

$So density of air at STP = \frac{molar mss}{molar volume}$ $"So density of air at STP "="molar mss"/"molar volume"$

$= \frac{28.969 \frac{g}{mol}}{22.4 \frac{L}{mol}} \approx 1.293 \frac{g}{L}$ $=(28.969g/"mol")/(22.4L/"mol")~~1.293g/L$

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Molar mass and density?

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.

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