If you carbonate water, and then expose the resulting soda water to the atmosphere and wait until it goes completely flat, will the (former) soda water end up more acidic in final equilibrium than water that was never carbonated and is also exposed to the atmosphere?
(Assume that both the water that was and was not carbonated are exposed to the exact same atmosphere, so that (a) they end up at the same temperature, and (b) the tiny addition to the level of atmospheric CO2 released during the carbonation process itself doesn't have any differential impact between the two waters.)
I understand that the soda water will be significantly more acidic than the flat water while it's still bubbly, because of the carbonic acid formed by the water and the injected pressurized CO2. I also believe that both waters will end up slightly acidic (although not as acidic as the soda water while it's still bubbly) because of the (modest) partial pressure of atmospheric CO2 in contact with both waters. My question is whether the high concentration of carbonic acid introduced into the soda water during the carbonation process permanently changes the equilibrium acidity of the water.
I'm also curious whether the answer would be different depending on whether you start with pure distilled water vs. "realistic" tap water, where the presence of impurities might somehow change the story.
My strong physical intuition is that the flattened (former) soda water will eventually "forget" about the carbonation and both waters will end up at the same equilibrium acidity, but some chemist friends disagree with me.