Soft Drinks

[bbarnes]

Why does soda 'fizz'?

 

[MrDudeMan]

CO2 is forced into a chamber with soda syrup at a cold temperature and this causes the CO2 to bind to the water and syrup molecules....why it fizzes, i do not know, but i know thats what the fizzing is, the CO2 bound to the molecules

sorry that wasnt helpful, just my .02 on the subject before the big boys arrive

 

[bbarnes]

so the CO2 is debonding from the molecules, or what?

 

[PowerMacG5]

The fizzing is caused because soda is not exactly water. It is the unsatble compund H2CO3 which breaks down into CO2 and H2O. This compound will break up when their is not an equilibrium between the pressure forcing into solution and the prressure forcing it out of sloution, or when the compound is disturbed. The reason soda fizzes when you shake it up is because, when you shake it, you disturb it. This causes the CO2 to break off of the H2O, and when you open the cap, it comes of with so much force that it causes the water to "blow apart" or spread apart. That is why when soda is flat (all the CO2 is removed) it does not fizz, because there is no CO2 to cause the water to move outward.

 

[Belegost]

Actually, while a small amount of the CO2 does bond with the water to form carbonic acid. (H2CO3) The carbonation is based around dissolving CO2 gas into the water, much like dissolving salt into water. Most of the CO2 (I think about 98%, but don't hold me to that figure) remains CO2, just dissolved in water. CO2 is dissolved in water at high pressures and low temperatures, but at atmospheric pressure tends to return to a gaseous state. The soft drink fizzes when you expose it atmospheric pressure as the CO2 energetically bubbles out of solution in the process lifting small particles of the liquid, the soft drink only fizzes visibly for a short time as the kinetics of the change in state slow as the concentration of carbon dioxide decreases. Overall the carbonic acid reaction does little in the bulk of the process, the concentrations of carbonic acid are quite low, a low equilibrium constant for the reaction.

If you replace the lid on the container the CO2 continues to bubble out until it reaches an equilibrium pressure with the CO2 trapped in the container. If allowed to sit the soft drink goes flat as the CO2 that was dissolved into the water returns to gas until the point at which the amount of CO2 remaining in the drink is equivalent to how much will naturally dissolve into water at atmospheric pressure.

Interestingly enough the ability for gases to dissolve into liquids is the basis for all fish life, the oxygen that dissolves into the water is what gills remove for the fish to live on. This also explains why thermal pollution of rivers and lakes has such a bad effect on aquatic life, the concentration of O2 dissolved in water is very temperature dependent, and the higher the temperature the less oxygen available.