Home Brew Forums > Calculation help for dissolved CO2

09-29-2012, 10:27 PM   #1
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Join Date: Sep 2012
Location: Clinton, MA
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 Calculation help for dissolved CO2

I have been searching all over and keep seeing the Henry's Law but I cant seem to get a formula together for what I am looking for.

I want to know how many grams of CO2 are in the soda based on the temperature of the soda and the pressure of the headspace (at equilibrium when no more CO2 is being absorbed into the solution). I then can use this for other formulations of interest, like how much I have actually used from the tank, the volume in the bottle as (3, 4, 4.5 ect).

I dont know if it is as simple as a I expect it should be, but if someone has the long hand down I could plug in the numbers that would be of great help. Also if they could explain the steps involved (or what each number represents)

I have created an excel formula, but that only worked if the temp was at 20C, not a variable temperature.

09-29-2012, 10:34 PM   #2
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Join Date: Sep 2012
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Here is what I have so far:

Lets say the pressure is 45 PSI (3.0612 atm) and the temp is 20 C.

C= Concentration of the dissolved gas in the solution
Kh = Henry's Law constant for the solution
P = Partial pressure of the gas above the solution

P = 3.0612 atm
Kh (This s=is where I would need the formula for a specific temp) (29.76?)
c = 2.4/29.76 = .01028 mol/L

1 mol = 44g
grams of Co2/Liter = 44 * .01028 = 4.5259

If the temp changes so does the grams/L.

The variable formula here is the 29.76 (Kh) and thats what I am having difficulty getting the formula down.

10-04-2012, 01:57 AM   #3
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Join Date: Sep 2012
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 formula

Well, after some more searching I found a formula that will tell me what pressure to set if I want a specific volume of CO2, and in turn from this I was able to get the grams using another formula, now onto the next step, getting the volume from Temp and pressure:

T= Temp in degrees F
V = Volume os CO2
P = 0.0101056*T+0.00116512*(T^2)+0.173354*T*V+4.24267* V-0.0684226*(V^2)

so if the Temp is 32 and the Volume is 4 then the pressure would be 22.235 PSI

I want to calculate for V based on the temp and pressure using this formula. I am ashamed to say it has been way too long since I have done math like this to do the whole cancelation method. If someone is good at at and can do it easy for me that would be appreciated, in the meantime I am going to try to knock it out myself.