Hullo! I'm working on a lab in chemistry regarding reaction rates, particularly through letting a reaction proceed on a mass balance and letting CO2 escape (I'm working with HCl and CaCO3). However, I've run into a bit of a problem while preparing...which is that I don't have any cotton stoppers. I tried googling for alternatives, but I haven't really come up with anything aside from the fact that most cotton balls sold in stores (at least in the USA); everything else is irrelevant and mostly food-related.
Is there anything I can find at a store that I can use as a stopper that would let gas escape? Would cotton balls (that are definitively made of cotton) be OK to use for this experiment?