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 STP. Assume ideal behavior and use two significant figures in your answers.

Answer 1

78 * 28 + 21*32 + 1*39.9. divided by 100.. you get average weight of gases. i.e molar mass of air =28.959=28.96. for second part,use shortcut of going through vapour density method. vapour density = moleculat weight/2=14.48. relative density= vapour density * density of hydrogen(0.089). = 1.29