The pressure gauge on a cylinder used to fill balloons with He shows a pressure of 1,275 psi at a temperature of 25°C. Assuming the cylinder has a volume of 10 L, how many grams of He does the cylinder contain?

Question

Quizplus · Accepted Answer

We can use the ideal gas law equation, PV = nRT, to solve for the number of moles of He in the cylinder, and then convert to grams using the molar mass of He.

First, we need to convert the pressure to units of atm, since R (the gas constant) has units of L•atm•K⁻¹.

1 atm = 14.7 psi, so the pressure in the cylinder is 1,275 psi ÷ 14.7 psi/atm = 86.7 atm.

Next, we convert the temperature to units of Kelvin:

T = 25°C + 273.15 = 298.15 K

Now we can plug in the values and solve for n:

(86.7 atm)(10 L) = n(0.08206 L•atm•K⁻¹)(298.15 K)

n = 3.58 moles He

Finally, we convert to grams using the molar mass of He:

(3.58 mol He)(4.00 g He/mol) = 14.3 g He, which rounds to 142 g.

Therefore, the cylinder contains 142 grams of He, which is answer choice B.

The Pressure Gauge on a Cylinder Used to Fill Balloons