Open a can of soda . . .

Open a can of soda at room temperature. Leave the can alone; don’t drink it. Keep it at room temperature. How long will it be until the soda is flat?

why would anyone want to know the answer to that?

Why is not important in The Straight Dope.

Not all carbonated drinks lose their fizz in the same amount of time. Cheerwine loses it in an incredibly fast time while pepsi and coke are quite slower.
Why not conduct your own experiment?

How flat is “flat?” I had a can of coke sitting around all afternoon – at least 4 hours, and it was still fizzy enough for me to drink. YMMV.

I totally agree!! When these sorts of questions hit, it’s time to do a quantifiable test!

Get 10 cans of soda and open them. Take careful measurements and report back to us!

HOW flat though. After 24 hours a coke still has some carbonic bite to it (compare it to coke which has been left out for several days.)

If you put a carbonated drink in a vacuum chamber and pump it down, it effervesces like crazy for awhile, then transitions to vacuum-boiling. Do this for just a few minutes, then take it out and taste it. It is FLAT. It’s like cola syrup in water.

Therefore I suspect that carbonation lasts much longer at sea level than at high altitudes (Denver, Mexico City, etc.)

Perhaps one way to quantify “flatness” would be to do pH tests. As the carbon dioxide (in the form of carbonic acid) is driven out of solution, the pH would rise.

Proposed experimental protocol:

  1. Open a Coke
  2. Do pH tests every hour or so until the pH stabilizes
  3. Plot the results
  4. Publish them on the SDMB
  5. Await a call from the ig-Nobel prize committee

Or if you are really lazy (and have the equipment) you can just put a pH sensor in there and hook it up to the computer, which will automatically chart and graph the data.

The air pressure of the room would be a factor, wouldn’t it?

Almost certainly. As would be temperature, the brand of soda, how the soda is packaged (canned or bottled), etc., etc.

You don’t want to do too much in the initial investigation. Once you have “promising results”, you can start making the grant applications for those further experiments…

I tend to think that 7Up goes flat alot faster than any other carbonated soda.

It seems like a couple hours after opening a 7Up, if you don’t seal it, it goes flat.

Anyone agree?

To shed some light here, not all sodas have the same amount of carbonation. And yes, it does depend on room temperature and air pressure. At low temps, gas is more soluable in liquids, and thus less likely to diffuse out of the solution. While we can vary temp more easily than air pressure, higher pressures would also slow down the diffusion of CO2 from the soda. Technically, it depends on the partial pressure of CO2 component in the air mixture which would dictate how much additional CO2 can diffuse out of the soda.

Graphically, I’d WAG the diffusion vs. curve would be a curve reaching 100% diffused (100% flat) asymptotically…although it would certainly taste totally flat with minimal sign of fizz. - Jinx