Problem No 3 Ideal Gas Law A 2ft3 closed tank is filled with

Problem No. 3 [Ideal Gas Law]

A 2-ft3 closed tank is filled with 0.30 lb (weight or force) of gas which is thought to be either oxygen or helium. A pressure gage attached to the tank reads 12 psi at T=80F. Is it He or O2? Indicate why.

Solution

Given

volume = 2 ft³ = 0.056 m³

Pressure = 12 psi = 82737.1 N/m²

Temperature = 80^o F = 299.817 K

weight of substance = 0.30 lb = 0.133446 N

mass of substance = 0.133446 *1000/9.8 = 13.616 g

According to ideal gas law

PV = (m/A) * RT

82737.1 *  0.056 = ( 13.616 / A ) * 8.314 * 299.817

A = 7.325

As atomic weight of He is aproximately 7.325 , Helium gas should be used.