Find the Oxygen Mass in a Welding Tank

[dereklin]

Homework Statement

A welder using a tank of volume 7.40×10−2m3 fills it with oxygen (with a molar mass of 32.0g/mol ) at a gauge pressure of 3.20×105Pa and temperature of 38.7∘C. The tank has a small leak, and in time some of the oxygen leaks out. On a day when the temperature is 22.9∘C, the gauge pressure of the oxygen in the tank is 1.60×105Pa .

Homework Equations

(a)Find the initial mass of oxygen.
(b)Find the mass of oxygen that has leaked out.

The Attempt at a Solution

(a)PV=nRT
n=PV/RT
m=n*32
link to calculations
answer I got: 0.29225 kg
this answer was incorrect

 

[ehild]

Welcome to PF.
Type in your calculation, please.
You used the gauge pressure instead of the pressure of the gas. Do you know what gauge pressure is?

 

[dereklin]

ok I see where I did wrong
Thanks for the help.