Forget the mass of the bottle, just pour the 250mL into a beaker, before I pour the drink into the beaker, I should weigh the beaker then 250ml+weight of beaker = mass before experiment. Then the mass difference e is CO2 lost.
We Basically weighed the whole bottle and then opened it, poured the contents into a beaker, reweighed the bottle, weighed 6g of , put it into the beaker, stirred it and waited 10 minutes. Reweighed the beaker and it contents. Then repeated the weighing after 30 minutes. Then you could calculate the mass of CO2 lost. :apig: