How much does CO2 weigh?

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BernardSmith

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I wonder if anyone in the forum can answer this question. If I am making say five gallons of wine from juice with a starting gravity of, say, 1.085 how much will the weight drop when all the CO2 has been degassed or has otherwise dissipated (assume no evaporation of the liquid)? (about 10.625 lbs of sugar)
 
That is a hard one to answer to be honest. You would be able to approximate by knowing your final gravity and using some stoich to figure out how many mols of CO2 that will give you. one you know that multiply that by the number Doctor gave you and you will know the mass difference from co2 loss.
 
In the fermentation process, for every molecule of glucose consumed, 2 molecules of CO2 are produced.
Five US gallons @1.085 = 4.276 kg sucrose. Sucrose is 342.30 g/mol, so you have 12.49 mol of sucrose. This gets converted into 2 molecules of glucose, so 24.98 mol glucose. There would thus be twice that amount - 49.97 mol - of CO2 produced @44.01 g/mol, so 2,199 kg CO2.

Initially, assuming you had a solution of 5 US gallon water plus 4.276 kg sucrose, the mass was (18.93L*1kg/L) + 4.276kg = 23.21 kg. The mass drop should thus be 9%.

Interestingly, it doesn't really match reality: We would also expect 2mol of ethanol per mol of glucose, so again, 49.97 mol ethanol @46.07 g/mol = 2302g @0.789g/ml = 2,917 liters. So %ABV should be roughly 2.917/18.93 = 15.4% ABV. Experimentally, it's rather 11.4%.

[taking this too seriously:] So if looking instead at the experimental data, 11.4%ABV is 2.16L ethanol/18.93L solution. 2.16L ethanol @0.789g/ml = 1704g @46.07g/mol = 36.99 mol. We should have about the same amount of CO2 produced (as said before, the fermentation process is: 1 mol glucose -> 2 mol CO2 + 2 mol ethanol). So 36.99 mol CO2 @44.01g/mol, 1.628 kg CO2 (again, ~9.3% mass drop) and that's what I'd bet on :p Please weight it before/after and report your results :) :b
 
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