Why does soda stay fizzy longer in an open can rather than a bottle?

"The fizziness of a soft drink comes from the gas carbon dioxide that is dissolved in the liquid. Whether the carbon dioxide stays in the liquid or evaporates into the air depends on the amount of air pressure pressing down on the liquid. At a normal atmospheric pressure, the carbon dioxide will evaporate completely, leaving your soda flat. This will happen if you leave your soda sitting out in a glass overnight- it will be flat in the morning.

In a can, the amount of pressure on the liquid is much greater, forcing the carbon dioxide to remain in the liquid. You can tell that the can is pressurized because it is very difficult to dent or deform a closed can. That's because the pressure is pressing out on your finger, making it keep the cylindrical shape. However, as soon as you open the can, the carbon dioxide starts to evaporate, losing its fizziness. It may seem like it stays fizzy in an open can, but will eventually go flat.

In a bottle, there is a lot more air in the bottle relative to the liquid. When you open a bottle, you are letting the pressure off. When you close it back up, some of the carbon dioxide from the Coke evaporates into the air in the bottle. It will continue doing so until carbon dixoide in the air in the bottle builds up the air pressure so much that it keeps any more carbon dioxide from evaporating."

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Another aspect of how long a carbonated drink will remain "fizzy" (containing dissolved CO2) has to do with relativity. Since the drink will "outgas" (the process of the CO2 coming out of solution) at a steady rate depending on the surrounding atmospheric pressure, if a quantity of liquid starts with more CO2 dissolved, it will retain CO2 longer. Early mass produced glass bottles had flaws and were known to explode if the liquid was forced to outgas by mechanical shaking (the liquid in motion forces CO2 out of solution) the bottles often exploded. Cans allowed more pressure to be added to the liquids without this drawback occurring. The invention of the plastic bottle, while not as strong as a can in resisting ruptures and explosions, does allow bottling at lower dissolved gas levels than the cans so therefore they complete outgassing quicker in the open environment.

https://en.wikipedia.org/wiki/Soft_drink