|MadSci Network: Chemistry|
I think you are right. If you look at the ingredients in a can of Pepsi One (it will be similar to regular Pepsi, except the regular stuff will have sugar or corn syrup or some type of sweetener like that, while Pepsi One has Aspartame (artificial sweetener)), you'll see carbonated water, caramel color, natural and artificial flavors, phosphoric acid, aspartame, citric acid, sodium benzoate, caffeine, and acesulfame potassium.
The carbonated water is simply water that has been pressurised with carbon dioxide, so that some carbon dioxide is dissolved in the water.
I don't expect that the other substances listed in the ingredient list will affect how much or how long carbon dioxide is dissolved in the water (that is, if you remove any one ingredient, the amount of carbonation in the soda should stay the same.).
Hence, we'll just consider a temperature effect (rather than what the ingredients might do...that would be called a "matrix effect"). The amount of carbon dioxide that the water can hold (dissolved) is dependent only upon the temperature of the water (it's like if you tried to dissolve sugar in room temperature water and in hot water. IN hot water, you can dissolve more sugar. Rock candy is made by dissolving sugar in hot water and cooling the water down. Then, the water can't hold as much sugar, and the sugar starts crystallizing on whatever surfaces are available).
If you freeze a can of soda and warm it up again, I'd expect that you'd have exactly the same amount of carbonation that is lost upon opening the can. Since carbon dioxide freezes much lower than water, it might be interesting to see how much carbonation remains in a soda if you open it while frozen and let it thaw.
By the way, have you ever dumped salt into a freshly poured glass of soda? Try it sometime.
I hope that I helped you understand your results. Please email me if you have further questions.
Try the links in the MadSci Library for more information on Chemistry.