If I ever new, I've forgotten

[Doug]

The other night my wife placed a bottle of soft drink in the freezer and forgot about it.
Lucky it was in a PET bottle so it did not burst and shatter.
My problem is that I can not recall why all the gas comes out when soft drink freezes. I keep thinking only that the solubility of gas in a liquid increases with a decrease in temperature, unlike solids such as salts.
I once placed a freshly opened can of Coke in a large necked thermos filled with liquid nitrogen and that too produced a spectacular fountain of Coke....messy, but spectacular.
Can anyone refresh my memory on why dissolved gas is driven off when the liquid in which it is dissolved gets colder?

cheers,
Doug

[Lee]

The dissolved gas is driven out of the liquid as it freezes - not as it gets colder - gases are more soluble in liquids as temperature falls. As the liquid freezes, gas leaves solution and forms bubbles. Gases are less soluble in the sold phase than the liquid.
If you leave the softdrink to thaw, it should be OK unless there has been a leak and the gas escapes while it is frozen....
My physics is rusty these days - but this is what I remember....

[Doug]

Thanks Lee,
its a bit late to leave the softdrink to thaw, it was like a volcano when I opened it.
What you say makes sense, I can see that as the liquid solidifies it will have diminished capacipty to disolve gas, but once disolved, I would have expected the gas to be held.
I guess the actual mechanics of solubility in liquids is a very involved area of study.
cheers,
Doug

[Doug]

I have been thinking further on this or at least trying to.
As I recall when a substance is dissolved in a liquid, it is transformed into its component ions. Probably badly expressed however....
So if, say for example some Sodium Chloride were to be dissolved in water we would have some Hydrogen ions, Oxygen ions, Sodium ions and some Chlorine ions, and since it is possible to have frozen salt water it is clear that the salt ions do not reassociate at freezing and precipitate out. This being the case, why do carbon and oxygen ions(CO2) reassociate at freezing? after all Sugar being a carbohydrate, when dissolved makes up or yields carbon ions as well as hydrogen and oxygen ions. There must be some as yet obscure(to me) mechanism that I am missing.
cheers,
Doug

[Lee]

You are not recalling correctly sorry..... Solutes (salts in this case) do dissolve into their component ions (depending on how soluble of course) - in sodium chlorides case - it dissolves into sodium (Na+) and chloride (Cl-) - not hydrogen, oxygen etc - to form hydrogen and oxygen from water you must break the covalent bonds between the hydrogen and oxygen - by passing electrons through it (electrolysis), or adding a strong oxidiser (like sodium metal for instance).
Water does exist in an equilibrium where it breaks into hydrogen ions (H+) and hydroxide ions (OH-), but only in very small amounts, mostly it exists as H2O.
With carbon dioxide - some is dissolved into the water as CO2, some forms carbonic acid H2CO3 - but the carbon and oxygen are always covalently bound in this case - they don't separate unless a chemical reaction causes them to.
Dissolving sugar into water just gives you dissolved sugar - again not the component hydrogen, carbon and oxygen.

[Doug]

Thanks Lee, I knew I was rusty on this stuff, but didn't realise I had corroded right through.
cheers,
Doug