If the total volume of gas collected is 5.50 L at a temperature of 25 ? C and a
ID: 791727 • Letter: I
Question
If the total volume of gas collected is 5.50L at a temperature of 25 ?C and a pressure of 762torr , how many moles of gas was in the bicycle tire?
The air in a bicycle tire is bubbled through water and collected at 25 ?C.
n_air = ??? mol
This is what i got:
Vtot = 5.50L
T=25 degree + 273 =298k
P = 762 Torr
I used used n=PV/RT
(762 Torr)(5.50L)
-------------------------------------- = 0.226 mol
(62.364 L*Torr/mol*k)(298k)
However I got it wrong!!
It says:
"The air was bubbled through water. You need to correct for the vapor pressure."
What is the correct answer for this? Please help me. Thank you
Explanation / Answer
Vapor pressure of water at 25 deg C = P(H2O) = 23.8 torr
P(gas) = P(total) - P(H2O)
= 762 - 23.8 = 738.2 torr
= 738.2/760 = 0.971316 atm
V = 5.50 L, T = 25 deg C = 298.15 K, R = 0.08206 atm.L/mol.K
Ideal gas equation: PV = nRT
Moles of gas = n = P(gas)V/RT
= 0.971316 x 5.50/(0.08206 x 298.15)
= 0.218 mol