Question

At STP, air can be considered to be a mixture of ideal gases: 21.0% O2, 78.0% N2, and 1.00% Ar by volume.

a. Calculate the partial pressure of each gas at STP.

b. Calculate the density of air in g L at STP.

Answer 1

STP conditions

P = 1 atm

T = 273 K

a)

partial pressure of O2 = 0.21 x 1 = 0.21 atm

partial pressure of N2 = 0.78 x 1 = 0.78 atm

partial pressure of Ar = 0.01 x 1 = 0.01 atm

b)

density of air = molecular mass / 22.4

                     = 28.8 / 22.4

                     = 1.29 g / L