Please help!! Number of oxygen molecules in a oxygen cylinder?
A tank of compressed oxygen gas at a doctor’s office has a pressure of 95 times atmospheric pressure. If the volume of the tank is 565 cm3, how many oxygen molecules does it contain?
I am having so much trouble with this. I tried using PV=nRT but I keep coming up with the wrong answer. I don’t know if I’m converting something wrong or what. Any help is greatly appreciated!
Okay so I tried this-PV=nRT
V=(565 cm^3)/(1000000)=5.65e-4 atm
(9625875 Pa)(5.65e-4 atm) = n(8.314 J/mol*K)(300 K)
n= 2.180506525 * 6.022e23
= 1.3131e24 molecules
I have no idea what I’m doing wrong here. I’ve tried to enter more & less sig figs as well. Please help!
You are using the correct equation, so just make sure to match all your units, and solve for n. You may find this website useful for picking an R that suits your units: http://en.wikipedia.org/wiki/Gas_constant
Remember that T is absolute temperature, too. Good luck!
Ok, let’s try this.
P = 95 atm
V = 565 cm^3
n = ?
R = 82.05746(cm^3 atm)/(K mol)
T = 273.15 K (not specified in problem, assumed ST(but not P, obviously)
OK, that gives us:
(95 atm)*(565 cm^3) = n*(82.05746 cm^3 atm K^-1 mol^-1)*(273.15K), solve for n
n = 2.395 mol * 6.022e23 particles/mol = 1.442e24 molecules
My answer and yours are only different by the different temperatures we used. What is the right answer supposed to be?
Office chair gas cylinder removal – Part 2.MPG