Air has an average molar mass of 29.0 g/mol.The density of air at 0.97 atm and 30.0°C is:
A)29.0 g/L
B)39.0 g/mL
C)1.13 g/L
D)1.35 g/mL
E)11.4 g/L

Question

Quizplus · Accepted Answer

We can use the Ideal Gas Law to solve for density.

PV = nRT

P = 0.97 atm (convert to kPa for consistency)
V = 1 mol (standard molar volume at STP)
n = 1 mol (since we have 1 mol of air)
R = 8.31 J/mol·K (gas constant)
T = 30.0°C = 303 K (convert to Kelvin)

Rearranging the equation to solve for density:

d = P/(RT/M)

M = m/n = 29.0 g/mol (given)

d = (0.97 atm * 101.3 kPa/atm) / (8.31 J/mol·K * 303 K / 29.0 g/mol)

d = 1.13 g/L

Air Has an Average Molar Mass of 29