# Chemistry of making carbonated water?

I've found guides online for making carbonated (soda) water at home using a CO2 tank, a regulator and a plastic bottle. The guides suggest using "ice cold" water, filling the bottle 1/2 to 2/3 full, but differ on how much to shake the bottle, how many times to refill the bottle and what pressure to fill the bottle to. I was wondering if someone could provide an explanation for what the effect of temperature, pressure and agitation plays on the carbonation process and what a best practice might be for making soda water at home on demand.

EDIT: A regulator tells you the pressure in the bottle--it doesn't tell you how much CO2 has entered the bottle. So my question is two parts: What's the "optimal" amount of CO2 per 1L H2O for a carbonated beverage and how do you tell when you've hit this amount? Say I have a 1L bottle filled with 0.5L H2O. At what pressure should the bottle be at 10°C for "optimum carbonation"?

Cheers

• I'm surprised that shaking is part of the process, since agitation usually shakes carbonation out of soda much faster (even under pressure, as a recently shaken soda shows upon opening). I would expect a gentler motion, swirling or rolling the bottle, to expose more water to the gas and mix the dissolved CO2 evenly. But then, perhaps staying at a higher pressure makes the difference - I suppose it has time to settle back into the liquid before it gets opened? Commented Sep 4, 2016 at 3:47
• Shaking definitely helps the CO2 go into solution. If you leave the regulator valve open and invert the bottle, bubbles will enter the bottle for a bit and then stop. Shake the bottle, a few more bubbles enter the bottle. Continue to shake and bubbles will continue to enter. What I'm curious about (what prompted my question) was: The regulator just tells you the pressure in the bottle, it doesn't tell you how much CO2 has entered the bottle. If I have a 1L bottle and 0.5L H2O, at what pressure should the bottle be at say 10°C for "optimum carbonation"? Commented Sep 4, 2016 at 5:40

CO2 actually dissolves better in cold water vs hot water. that's why warm soda bottles will usually look more bubbly inside. Shaking the bottle greatly increases the surface area of interaction between water and gas, helping to speed up the process of carbonation.

First you must understand what the regulator does. If you set it for 20 lbs/sq inch then as CO2 dissolves into the water the regulator will release more CO2 from the high pressure tank to keep the gas pressure at 20 lbs/sq. inch.

CO2 actually dissolves better in cold water vs hot water. This is an equilibrium condition.

More CO2 dissolves into the water as the pressure is increased. This is an equilibrium condition.

Shaking increases the surface area of the water so the CO2 will dissolved into the water faster. For a given temperature and pressure though only so much CO2 will dissolve into the water. Shaking the water won't make "more" CO2 dissolve into the water, it will only make the water/CO2 system come to equilibrium faster.

Only a partial answer - a gas is more soluble in cold water.
(solid is more soluble in hot liquid)