What mass of helium is contained in the cylinder?

Question

A gas cylinder that contains helium has an internal volume of 6.88 L.6.88 L. A pressure gauge attached to the cylinder reads 2110 psi2110 psi (1 atm =14.7 psi)(1 atm =14.7 psi) at 23.9 ∘C.23.9 ∘C.

What mass of helium is contained in the cylinder?

Answer 1

Use the ideal gas law: PV = nRT and solve for n (moles). Then convert moles to grams using the atomic mass of He(4 g/mol).

P = pressure = 2110 psi x 1 atm / 14.7 psi = 144 atm

V = volume = 6.88 L

n = moles = ?

R = gas constant = 0.0821 Latm/Kmol

T = temperature in K = 23.9C + 273 = 302K

n = PV/RT

n = (144)(6.88) / (0.0821)(302)

n = 39.95 moles

mass = 39.95 moles x 4 g / mol = 160. g (3 sig. figs.)