# (19-74) Ideal gas problem

1. Dec 9, 2011

### qspartan570

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

An oxygen cylinder for medical use contains oxygen at a pressure of 140 atm, at room temperature (20$\circ$C). The cylinder measures 20 cm in diameter and 110 cm in length. How many kilograms of oxygen does this cylinder contain? What will be the volume of the oxygen if it is allowed to expand slowly to normal atmospheric pressure, at room temperature?

2. Relevant equations

ideal-gas law pV=nRT
pV=NkT

3. The attempt at a solution

Vcylinder= ∏r2h=(∏)(10 cm)2(110 cm)=3.45 cm3

moxygen= 3.45 cm3 X 1.141 g$\bullet$cm3=3.94 g or 0.00394 kg

According to the book the answer to this part is 6.4 kg

What did I do wrong?

2. Dec 9, 2011

### ehild

Take care of the units, and recalculate the volume.
How did you get the mass? Note that the density of gases depend on pressure and temperature.

ehild