Dry nitrogen is pumped into a glove box to protect an oxygen-sensitive experimen

Question

Dry nitrogen is pumped into a glove box to protect an oxygen-sensitive experiment inside. The box is maintained at a slight positive pressure of 6 in. H2O to prevent air from backdiffusing into the box through a vent line. Let’s say we connect the box to a standard-size gas cylinder (1.75 ft3 - initially filled to 3000 psia N2). If the gas contents of the box must be replaced every 10 minutes and the box is 1 m3 (sitting in a 25 °C lab), how much N2 flow is required in g/min? How long will the gas bottle last? Perform your calculations assuming that nitrogen is: (a) an ideal gas.

Explanation / Answer

N2 gas cylinder :

V = 1.75 ft3 = 0.0496 m3  

P = 3000 psia = 204.14 atm = 2.06845 x107 Pa

T = 25 DegC = 298 K

Heence moles of N2 in the cylinder, n = PV/RT = (2.06845 x107 Pa x 0.0496 m3 ) / 8.314 Jmol-1K-1 x 298K

= 414.1 mol N2

Molecular mass of N2 = 28 g/mol

Hence mass of N2 inside the cylinder = 414.1 mol N2 x28 g/mol = 11595 g

Glove box :

V = 1 m3  

P = 6 in. H2O = 0.0147352 atm = 1493 Pa

T = 25 DegC = 298 K

Moles of N2 gas required to maintain 6 in. H2O pressure, n = PV/RT

= (1493 Pa x 1 m3 ) / (8.314 Jmol-1K-1 x 298K)

= 0.603 mol N2

Hence mass of N2 = 0.603 mol N2 x 28 g/mol = 16.9 g

Now 16.9 g N2 needs to be repalced in every 10 min.

Hence mass of N2 flow required per minute = 16.9g /10 g = 1.69 g N2/min (answer)

16.9 g N2 lasts for 10 minute

Hence 11595 g of N2 that will last = (10 min / 16.9 g ) x 11595 g = 6861 min (answer)

Related Questions

Navigate

• Browse (All)
• Browse D
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.