|MadSci Network: Chemistry|
That's not a terribly easy question to answer, and I feel it may be best to actually try and determine that experimentally. In theory the solution phase would be more efficient, as you will also dissolve some of the CO2 to form carbonic acid, but in practice the low concentration may not be as efficient. Also, if you bubble the CO2 through a solution you are guaranteeing that the CO2 will have to travel through your reagent, whereas with a powder it may not come into contact. Therefore I would suggest using a solution.
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