Question

how to calculate the molar mass of air given that 78.88% N, 20.94% O, and .97% Ar. I did .7808(14.01)+.2095(16.00)+.0097(39.95)= 14.68 which is apparently not the way to do it. Thank you

Answer 1

Air is the mixture of gases , the molar mass of which can be calculated by multiplying the mole fractions of each component by its molar mass.

The method applied by you is absolutely correct, the only mistake that you have made is using the atomic masses of nitrogen and oxygen .

The molecular masses of nitrogen as 28.02 and that of oxygen as 32.00 should be used.

So the molar mass of the air is given as :

= 0.7888 (28.02) + 0.2094(32.00) + 0.0097(39.95)

= 22.1 + 6.7 + 0.39

= 29.19 g/mol