# Calculating the volume of gas in the same canister from 2 locations.

1. Jul 3, 2012

### LAB

I have a canister with a capacity of 8334cm3, if the canister is sealed at ambient atmospheric pressure (1016.5hPa, 25.6 deg/C) at one location then transported thousands of kilometres where the ambient pressure and temperature (1014.5hPa, 20.5 deg/C) is different.

I then connected my canister to an inverted measuring cylinder over a water bath to physically measure the difference in the volume of gas in the canister, I got a reading of -700mL (started at 1000mL finished at 300mL).

How do I mathematically calculate the difference in volume of gas in the canister in mL's ?

2. Jul 3, 2012

### Nessdude14

You'd use the ideal gas law, PV=nRT
P is pressure, V is volume, n is number of molecules of substance in mols, R is the ideal gas constant (8.31 J/mol K) and T is Temperature (in Kelvin).

From the parameters you measured, you can rearrange the equation to determine the number of mols of substance in your container.
n=(PV)/(RT)

If you then want to know the volume of that container for a given pressure and temperature, you can again rearrange the equation:
V=(nRT)/P
and as long as the container remains sealed, n should remain constant.

However, this does assume that no gas was able to permeate your container (which is nearly impossible in reality).

Last edited: Jul 3, 2012
3. Jul 3, 2012

### LAB

Thank you Nessdude14,

After doing the calculation according to the Ideal Gas Laws sugested, the volume of gas at location 2 with lower temperature and pressure equals ~154mL less than location 1, but when I physically measured it; the result was 700mL less.

Can anyone sugest why this is happened? or did I calculate it in correctly?

4. Jul 4, 2012

### CWatters

How was the gas transported and in what?

If by air then gas might have leaked out due to the reduced cabin/hold pressure in flight. As you descended the increasing pressure might have resealed the container (eg gas inside now stuck at the lower cabin pressure). Hence much lower volume when measured.

If the canister is a special gas bottle then this is unlikely to be the cause - unless it wasn't sealed properly?