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Q & A: densely carbonated Baloney

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Most recent answer: 04/15/2011
Q:
http://www.ehow.com/facts_6925741_density-carbonated-water.html
What's the density of carbonated water? see also http://answers.yahoo.com/question/index?qid=20070108143249AA74xzY They say that you can calculate the density of carbonated water (say 1% CO2)by taking a weighted average of the density, 99% the density of water and 1 % the density of CO2 gas.
- Mike W
A:
Both sites say, in very similar words, that the way to calculate the density of water with 1% carbonation (by molecular concentration, it seems) is to take the weighted average:

 0.99*density of water +0.01*density of CO2 gas.

 They get that dissolved CO2 reduces the density by almost 1%, since  the density of CO2 gas is very low compared to water at atmospheric pressure.

It's a comical example of two bad habits:
1. copying other web sites thoughtlessly.
2. using formulas thoughtlessly.



They aren't even remotely close to getting the description right. The dissolved CO2 isn't there as a bunch of little pockets of CO2 gas. It's there as individual molecules and ions (some ionizes). Since CO2 has a molecular weight about 2.5 times as big as H2O, but doesn't occupy all that much more space, it actually raises the density, rather than lowering it. From looking up the experimentally observed partial molar volume of CO2 in water, I get that instead of the density going down almost 1% for every 1% carbonation, it actually goes up about 0.37%.

Mike W.

(published on 04/15/2011)

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