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# Measuring PH as a poor man's CO2 meter

## Measuring PH as a poor man's CO2 meter

(OP)
Hi!
So I'm working on a small project currently in which we are carbonating tap water. We don't have a proper CO2 meter in our lab, and this project's budget does not have the space to buy one. However, my understanding is that rapid cabonization of water via CO2 gas will produce a byproduct of carbonic acid, thereby raising the overall acidity of the solution.

My question is: If I closely monitor initial volume, temperature, and PH of my fluid, can I get an accurate measurement of CO2 content in water after we treat it with pressurized CO2 gas- derived from the change in PH?

PH seems like the most logical/practical variable available to me, but how about any other variable that I can pull a number from? I'd love to find a graph or equation that will show such a correlation.

Thanks for any suggestions!
-k

### RE: Measuring PH as a poor man's CO2 meter

Carbon dioxide dissolved in water at a low concentration (0.2%–1.0%) creates carbonic acid (H2CO3),[2] which causes the water to have a slightly sour taste with a pH between 3 and 4.

The amount of a gas like carbon dioxide that can be dissolved in water is described by Henry's Law. Water is chilled, optimally to just above freezing, in order to permit the maximum amount of carbon dioxide to dissolve in it. Higher gas pressure and lower temperature cause more gas to dissolve in the liquid. When the temperature is raised or the pressure is reduced (as happens when a container of carbonated water is opened,) carbon dioxide comes out of solution, in the form of bubbles.

The quality of carbonated beverages including soft drinks, seltzer and beer is affected by the dissolved CO2 (the gas that causes carbonation) and the amount of carbonic acid in the drink. Carbon dioxide (CO2) has an infrared absorption wavelength of 4.27 micrometers and can be measured online using an infrared carbonation sensor. This is an improvement to the traditional inferred measurement method using temperature and pressure for Henry's Law coefficients because this methodology is influenced by changes in density and alcohol content. Infrared measurements are not affected by changes in density or alcohol content because they are actually measuring the CO2 molecule using the infrared transmissivity of the solution.

The amount of carbonation in a beverage is measured by weight per unit volume (grams/liter). This is because introducing CO2 into a beverage will change its weight. An easy experiment to prove this is to take a seltzer bottle and weigh it. Carefully remove the top slowly so no liquid escapes from the bottle; as the gas escapes the weight of the bottle of seltzer will go down

http://chemistry.wikia.com/wiki/Carbonation

### RE: Measuring PH as a poor man's CO2 meter

(OP)
thanks! I did read that bit- I guess I was looking for a graph or calculation/calculator which would estimate content based on PH. I hadn't noticed the weight change though, I would be surprised if I could get a fine enough measurement to effectively determine content. I guess if I just scaled up my volumes enough. I did recently find this, so maybe I've answered my own question at this point.

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