[ch3m15try]

All I've got. Don't know whether CO2 should be treated as an ideal gas or anything.   Any help? Thanks.  

(Americans note these are metric tonnes!)

[Arkcon]

If this is a class problem given to you while, or slightly after, the classroom discussion on Ideal Gases, then yeah, you probably should treat it just like that.  You shouldn't wonder if CO₂ is an ideal gas, because no gas is ideal.  You should just get started on the calculations, and maybe if you're still feeling pedantic, say "Assuming CO₂ is an ideal gas"  At any rate, you'll be in the ballpark for ordering that balloon made.

[Dan]

The main problem is that you need to know what the pressure inside the balloon is, and considering pV=nRT, the interplay between p and V will depend on  the elasticity of the rubber. You need to know the maximum pressure that the balloon can withstand before it pops.

[fledarmus]

Unless it is expressly given, you generally have to assume in balloon problems that the pressure inside the balloon is slightly but negligibly higher than the pressure outside.

[AWK]

Balloon filled with CO2 never leave surface of eartH, but big balloon filled with helium can do it.