Finding the density

Question

8. Calculate the density of propane gas, C3H8, at 20.0oC and 1.15 atm? 2 marks.

Answer 1

Density = mass / volume

For a gas, we can use the ideal gas law to find the mass, and if we assume a volume of 1 L, we then have what is needed to find the density.

PV = nRT

P = pressure = 1.15 atm

V = volume = 1 L

n = moles = ?

R = gas constant = 0.0821 Latm/Kmol

T = temperature in K = 20ºC + 273 = 293K

Solving for n (moles) we have ...

n = PV/RT = (1.15)(1) / (0.0821)(293)

n = 0.0478 moles of propane

molar mass of propane (CH₃CH₂CH₃) = 44.1 g/mol

mass of propane = 44.1 g / mol x 0.0478 mols = 2.11 g

Density = 2.11 g / L