Untitled - Kelly Walsh High School

84 CHEMISTRY FOR THE UTTERLY CONFUSED
Don’t Forget!
Quick Tip
The oxygen gas that forms occupies a volume of 550. mL at 27C. The atmospheric
pressure is 731.3 torr.
In using any of the gas laws, be sure to express the temperature in Kelvin.
At this point, you now have 550. mL of oxygen gas at 731.3 torr and 300. K
(27 o C 273). From this data, you can use the ideal gas equation to calculate the
number of moles of oxygen gas produced:
PV nRT
n PV/RT
You will need to convert the pressure from torr to atm:
(731.3 torr) (1 atm/760.0 torr) 0.9622 atm
and express the volume in liters: 550. mL (1 L/1000 mL) 0.550 L
Now you can substitute these quantities into the ideal gas equation:
n (0.9622 atm) (0.550 L)/(0.0821 Latm/Kmol) (300. K)
n 0.021486 mol O 2 (unrounded)
Be sure, especially in stoichiometry problems involving gases, that you are calculating
the values such as volume and pressure of the correct gas. You can
avoid this mistake by clearly labeling your quantities that means, mol of O 2
instead of just mol.