Question

Validate that air has molecular weight of 28.97kg/(k mol).

Answer 1

Air composition: 78 % N₂, 21 % O₂ and 1 % Ar.

M(O₂) = 32 g/mol

M(N₂) = 28 g/mol

M(Ar) = 40 g/mol

$M(Air) = 28 \times 0.78 + 32 \times 0.21 + 40 \times 0.01 = 21.84 + 6.72 + 0.4 = 28.96 \;g/mol \;or\; kg/(k\;mol)$