# Keeping an open, partially empty soda bottle bubbly longer

I remember as a kid being able to get a little pump which you could screw onto a half empty soda bottle (I believe the bottles were glass at the time) to pump air into it to keep it fizzy for longer. I surmised or was told that this worked by increasing the density of the air, thus making it harder for gas to leave the liquid and enter the air.

I now find myself with partially empty soda bottles. Can I keep the fizz longer by squeezing the air out of the bottles and screwing on the lid? (My guess would be that this would work if the compressed bottle is altered such that it does not try and reform back to its original round shape, but if it would pop back save for the lid being screwed on, I'm actually going to make it loose its fizz slightly faster ?)

The fizz is dissolved carbon dioxide (or carbonic acid with which it is in equilibrium) which is put into the bottle under quite some pressure (around $\pu{120 kPa}$ at $\pu{4 ^\circ C}$ or $\pu{250 kPa}$ at $\pu{20 ^\circ C}$; from a first glance on the google results). $$\ce{CO2 (g) + H2O (aq) <=> H2CO3 (aq)}$$
Because the bottle (in first approximation) is a closed system, there is an established equilibrium between the "air" in the bottle (gaseous $\ce{CO2}$) and the dissolved $\ce{CO2}$. Once the bottle is opened the equilibrium is disrupted and the dissolved carbon dioxide is no longer as soluble as before.