Question

The air in a bicycle tire is bubbled through water and collected at 25 ∘C. If the total volume of gas collected is 5.25 L at a temperature of 25 ∘C and a pressure of 737 torr , how many moles of gas was in the bicycle tire?

Answer 1

As the gas bubbles through water, water vapor moves into the air. At 25˚C, the water vapor pressure = 23.8 mm Hg = 23.8 torr

The actual pressure due to the gas = 737 – 23.8 = 713.2 torr


At STP, 1 mole has a volume of 22.4 liters. Let’s convert back to STP and determine the volume at STP, using the equation below.

P1 * V1 / T1 = 760 * V2 / 273
P1 = 713.2 torr
V1 = 5.25 L
T1 = 25 + 273 = 298˚K

713.2 * 5.25/ 298 = 760 * V2 / 273
V2 = 4.51 Liters
Number of moles = 4.51 ÷ 22.4 = 0.2013