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Carbon Dioxide Solubility and Ice
Name: Steve
Status: student
Grade: 9-12
Country: United Kingdom
Date: Winter 2009-2010
Question:
What happens to the solubility of carbon dioxide in water
when the water is frozen. I did this to a bottle of soda pop and
when I opened it, there was a lot of fizzing which means the CO2 is
not soluble.
Replies:
Steve,
If we look at the solubility of CO2 in water as a function of
temperature, we find that solubility actually increases. Here is the
first graph I could find showing that:
http://www.rocketscientistsjournal.com/2006/10/_res/CO2-06.jpg
When water turns to ice, this is no longer an issue of solubility
but a measure of how much CO2 can be physically trapped in the ice.
Unfortunately, the amount of CO2 trapped in the ice will depend very
strongly on the conditions of freezing. Are the ice crystals formed
very slowly so that the CO2 is pushed out of the system? Did ice
form on top of the liquid first trapping most of the dissolved CO2?
Was the system agitated? etc. It would be very hard to predict
physical trapping.
Moreover, fizzing is not a good measure of how much CO2 was trapped.
Fizzing can result from agitation, small crystals becoming
nucleation points for bubble formation, etc.
I do not think we can answer this question because the term
solubility does not apply and the "measure" of fizzing is not a very
good indicator of solubility.
Greg (Roberto Gregorius)
Canisius College
You have several processes going on here. First, as the temperature
DECREASES the solubility of CO2 in water INCREASES. However, the solubility
of CO2 in ice essentially ZERO. So the same amount of CO2 is "forced" to
dissolve in a decreasing amount of water, which increases the pressure,
because it is confined to the space available (Henry's Law). When you
release the pressure, the CO2 / Soda will come to a new set of conditions,
namely atmospheric pressure. That is the fizzing you observe. Additionally,
as the CO2 evaporates rapidly heat is lost and you may observe soda
freezing, which feeds back into the cycle. Evaporation costs heat energy.
What you ask does not have a simple answer-- many "things" are going on.
Vince Calder
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Update: June 2012
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