CO2 tank question (converting mass to volume, oddly enough)?

Question

I am attempting to build a pneumatic propulsion system for a small ROV, which, as one would expect, uses a measurable volume of gas. However, all CO2 tanks I can find are rated in either ounces, grams, or pounds. How can I convert mass to volume, given known pressure?

Answer 1

Some CO2 cannisters can store CO2 in liquid form also.

If the CO@ is stored as a liquid the cannister lasts much longer and the outlet pressure of the gas is relatively constant and does not change very fast as the liqid boils off.

As the CO2 is used up the pressure decrease causes more gas to boil off from the liquid thereby maintaining a relatively constant pressure at the outlet of the cannister. This is also how the CO2 cartridges used in pellet and air guns work. They are filled with liquid CO2.

If they were filled with CO2 gas the pressure would decrease every time a shot was fired, and the cannisters would not last very long.

Liquid CO2 has a density only 1.03 times that of water.

Answer 2

PV=NRT

This is the ideal gas expression.

PV/RT = N

Molecular Mass = Molar Mass/ N

If you have a known mass, say, 28 g.  And CO2 is around 48g/mol, multiply:  28g(1 mol/48g) to get the number of moles of CO2.

If you work backward, you will have volume.

V=NRT/P