How Many Moles of Gas Are in the Bicycle Tire?

[ttiger2k7]

Homework Statement

The air in a bicycle tire is bubbled through water and collected at 25 $$^\circ {\rm C}$$. If the total volume of gas collected is 5.25 L at a temperature of 25 $$^\circ {\rm C}$$ and a pressure of 734 torr, how many moles of gas was in the bicycle tire?

Homework Equations

PV = nRT
$$n=\frac{PV}{RT}$$

R = .08206

The Attempt at a Solution

1. Convert 734 torr to atm

734/760 = .966 atm

2. Convert 25 $$^\circ {\rm C}$$ to K = 298.15 K

3. Plug those all in:

$$n=\frac{(.966 atn)(5.25 L)}{(.08206)(298.15 K)}$$

I got n=.207 moles, but the online assignment says I got it wrong.

 

[Borek]

0.207 is a correct number of TOTAL moles. Part of this total is water vapour.

 

[Blueshift5]

Your solution is correct, however, it is important to note that the units for pressure and volume must be consistent with the units of the gas constant, R. In this case, R is given in units of L*atm/mol*K, so the pressure should be in atm and the volume in liters. Therefore, the correct solution would be:

n=\frac{(.966 atm)(5.25 L)}{(.08206)(298.15 K)} = 0.207 moles

Make sure to always check the units and conversions when using the ideal gas law equation.