# Homework Help: Ideal Gas Law (mass)

1. Dec 5, 2011

### physgrl

1. The problem statement, all variables and given/known data

A fixed mass of oxygen (O2, molecular mass = 32 g/mol) is contained in a cylinder whose volume is 2.80 liters. The pressure is 148 atm when the temperature is 23oC. Find the mass of oxygen in the cylinder.

a. 20 g
b. 80 g
c. 140 g
d. 280 g
e. 546 g

2. Relevant equations

PV=nRT
m=n*molar mass

3. The attempt at a solution

148atm*2.80L=n*8.314*296.15
n=0.17 moles

m=n*molar mass
m=0.17*32
m=5.5g

and that is not a possible answer :s

2. Dec 5, 2011

### technician

Units again!!!!!

3. Dec 5, 2011

### physgrl

hehe thanks :s
is the pressure supposed to be in Pa then??

4. Dec 5, 2011

### technician

Has to be!!!!!!

5. Dec 5, 2011

### Liquidxlax

It's good to remeber that nearly everythig in thermodynamics has to be in energies which are in joules which are N*m

6. Dec 5, 2011

### physgrl

thank you!! :)

7. Dec 5, 2011

### physgrl

is the only wrong unit the pressure one??
because now i am getting 558g

8. Dec 5, 2011

### technician

you should have volume in m^3